Nonvolatile memory device and method for manufacturing same

ABSTRACT

A nonvolatile memory device includes: a first conductive layer; a second conductive layer; a first resistance change layer provided between the first conductive layer and the second conductive layer and having an electrical resistance changing with at least one of an applied electric field and a passed current; and a first lateral layer provided on a lateral surface of the first resistance change layer and having an oxygen concentration higher than an oxygen concentration in the first resistance change layer

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2009-139529, filed on Jun. 10,2009; the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the invention relate generally to a nonvolatile memorydevice and a method for manufacturing the same.

2. Background Art

A resistance change memory has been drawing attention as anext-generation nonvolatile memory because it is less prone tocharacteristics degradation despite downscaling, and easily increased incapacity (see, e.g., JP-A 2007-184419 (Kokai)).

The resistance change memory is based on the characteristics of aresistance change film whose resistance changes when a voltage isapplied to and a current is passed in the resistance change film. Such aresistance change film is made of various oxides, such as oxides oftransition metals.

Conventional resistance change films require an initialization process(forming) for decreasing the resistance thereof, and hence areinefficient. Furthermore, forming requires a high forming voltage, whichmay destroy the resistance change film. Moreover, the switchingoperation (reset operation) for switching from the low-resistance stateto the high-resistance state requires a large current, which makes itdifficult to reduce power consumption.

In this context, a method for facilitating the reset operation by usingan oxygen-rich composition on the anode side of the resistance changefilm to advance anodic oxidation is proposed in Z. Wei, Y. Kanzawa, K.Arita, K. Katoh, K. Kawai, S. Muraoka, S. Mitani, S. Fujii, K. Katayama,M. Iijima, T. Mikawa, T. Ninomiya, R. Miyanaga, Y. Kawashima, K. Tsuji,A. Himeno, T. Okada, R. Azuma, K. Shimakawa, H. Sugaya, T. Takagi, R.Yasuhara, K. Horiba, H. Kumigashira, and M. Oshima, IEDM2008, pp.293-296. However, even in this method, the reset current is notsufficiently reduced. In particular, with the downscaling of the device,the effect of reset current reduction is decreased, leaving room forimprovement.

SUMMARY

According to an aspect of the invention, there is provided a nonvolatilememory device including: a first conductive layer; a second conductivelayer; a first resistance change layer provided between the firstconductive layer and the second conductive layer and having anelectrical resistance changing with at least one of an applied electricfield and a passed current; and a first lateral layer provided on alateral surface of the first resistance change layer and having anoxygen concentration higher than an oxygen concentration in the firstresistance change layer.

According to another aspect of the invention, there is provided anonvolatile memory device including: a first conductive layer; a secondconductive layer; a first resistance change layer provided between thefirst conductive layer and the second conductive layer and having anelectrical resistance changing with at least one of an applied electricfield and a passed current; and a first lateral layer provided on alateral surface of the first resistance change layer and including anoxide of an element having a smaller absolute value of standard freeenergy of oxide formation than an element except oxygen contained in anoxide included in the first resistance change layer.

According to still another aspect of the invention, there is provided amethod for manufacturing a nonvolatile memory device, including:stacking, on a substrate, a first conductive film serving as a firstconductive layer, a resistance change film having electrical resistancechanging with at least one of an applied electric field and a passedcurrent, and a second conductive film serving as a second conductivelayer; etching the first conductive film, the resistance change film,and the second conductive film to form a lateral surface of theresistance change film; and oxidizing the lateral surface to make anoxygen concentration on a side of the lateral surface higher than aoxygen concentration in a center portion of a cross section of theresistance change film cut along a plane perpendicular to a stackingdirection of the stacking.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to a firstembodiment;

FIG. 2 is a schematic view illustrating characteristics of thenonvolatile memory device according to the first embodiment;

FIGS. 3A and 3B are schematic cross-sectional views illustrating thecharacteristics of the nonvolatile memory device according to the firstembodiment;

FIGS. 4A to 4D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing the nonvolatilememory device according to the first embodiment;

FIG. 5 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to a secondembodiment;

FIGS. 6A to 6D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing the nonvolatilememory device according to the second embodiment;

FIG. 7 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to thesecond embodiment;

FIGS. 8A to 8C are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a thirdembodiment;

FIGS. 9A to 9F are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a fourthembodiment;

FIGS. 10A to 10F are schematic cross-sectional views illustrating theconfigurations of other nonvolatile memory devices according to thefourth embodiment;

FIGS. 11A to 11E are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the fourth embodiment;

FIGS. 12A to 12F are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a fifthembodiment;

FIGS. 13A to 13F are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing another nonvolatilememory device according to the fifth embodiment;

FIGS. 14A and 14B are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a sixthembodiment;

FIGS. 15A to 15D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the sixth embodiment;

FIGS. 16A and 16B are schematic cross-sectional views in order of theprocess, illustrating a method for manufacturing another nonvolatilememory device according to the sixth embodiment;

FIGS. 17A and 17B are schematic cross-sectional views illustrating theconfiguration of a nonvolatile memory device according to a seventhembodiment;

FIG. 18 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theseventh embodiment;

FIGS. 19A and 19B are schematic cross-sectional views illustrating theconfigurations of other nonvolatile memory devices according to theseventh embodiment;

FIG. 20 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to an eighthembodiment;

FIG. 21 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theeighth embodiment;

FIG. 22 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theeighth embodiment;

FIGS. 23A to 23C are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a ninthembodiment;

FIGS. 24A to 24C are schematic views illustrating the configuration of anonvolatile memory device according to a tenth embodiment;

FIG. 25 is a schematic perspective view illustrating the configurationof another nonvolatile memory device according to the tenth embodiment;

FIGS. 26A to 26F are schematic cross-sectional views in order of theprocess, illustrating a method for manufacturing a nonvolatile memorydevice according to the tenth embodiment;

FIGS. 27A to 27E are schematic cross-sectional views in order of theprocesses continuing from FIG. 26F; and

FIG. 28 is a flow chart illustrating a method for manufacturing anonvolatile memory device according to an eleventh embodiment.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with reference to thedrawings.

The drawings are schematic or conceptual. The relationship between thethickness and the width of each portion, and the size ratio between theportions, for instance, are not necessarily identical to those inreality. Furthermore, the same portion may be shown with differentdimensions or ratios depending on the figures.

In the specification and the drawings of the application, the samecomponents as those described previously with reference to earlierfigures are labeled with like reference numerals, and the detaileddescription thereof is omitted as appropriate.

First Embodiment

FIG. 1 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to a firstembodiment of the invention.

A nonvolatile memory device D101 according to this embodiment isillustratively a cross-point nonvolatile memory device. The entireconfiguration of the cross-point nonvolatile memory device is describedlater. In the following, a description is given of a memory layer, whichis a relevant part of the nonvolatile memory device. The memory layerconstitutes one cell (memory unit) in the nonvolatile memory deviceD101.

As shown in FIG. 1, a memory layer 60 of the nonvolatile memory deviceD101 includes a first conductive layer 101, a second conductive layer102, a resistance change layer 111 (first resistance change layer)provided between the first conductive layer 101 and the secondconductive layer 102, and a lateral layer 112 (first lateral layer)provided on the lateral surface of the resistance change layer 111.

The resistance change layer 111 is a layer whose electrical resistancechanges with at least one of the electric field applied thereto and thecurrent passed therein.

The lateral layer 112 is a layer having a higher oxygen concentrationthan the resistance change layer 111.

The first conductive layer 101 and the second conductive layer 102described above are interchangeable.

In the following, the stacking direction of the first conductive layer101, the resistance change layer 111, and the second conductive layer102 is referred to as a Z-axis direction. Furthermore, one of thedirections perpendicular to the Z-axis direction is referred to as anX-axis direction, and the direction perpendicular to the Z-axisdirection and the X-axis direction is referred to as a Y-axis direction.

The resistance change layer 111 is illustratively made of a metal oxideof a transition metal. The lateral layer 112 is made of a metal oxidecontaining the metallic element used in the resistance change layer 111and having a higher oxygen concentration than the resistance changelayer 111.

The resistance change layer 111 can illustratively be made of a binarymetal oxide represented by M_(x)O_(y) (where M is a transition metalelement and O is oxygen), a ternary metal oxide represented byA_(α)M_(β)O_(γ) (where A and M are transition metal elements and O isoxygen), or a quaternary or higher metal oxide.

In the case where the resistance change layer 111 is made of M_(x)O_(y),the lateral layer 112 can be made of M_(x1)O_(y1) (y1>y). In the casewhere the resistance change layer 111 is made of A_(α)M_(β)O_(γ), thelateral layer 112 can be made of A_(α1)M_(β1)O_(γ1) (γ1>γ).

Here, in the case where the resistance change layer 111 is made ofM_(x)O_(y), transition metals other than the transition metal M may beadded to the lateral layer 112 in addition to M_(x1)O_(y1) (y1>y).Likewise, in the case where the resistance change layer 111 is made ofA_(α)M_(β)O_(γ), transition metals other than the transition metals Aand M may be added to the lateral layer 112 in addition toA_(α1)M_(β1)O_(γ1) (γ1>γ).

That is, it is only necessary that the oxygen concentration in thelateral layer 112 is higher than that in the resistance change layer111. In other words, it is only necessary that the oxygen concentrationin the lateral layer 112 is higher than that in the resistance changelayer 111 so that the lateral layer 112 can release oxygen more easilythan the resistance change layer 111 and supply oxygen to the resistancechange layer 111.

For instance, the lateral layer 112 can be made of a metal oxide havinga stoichiometric or nearly stoichiometric composition ratio, and theresistance change layer 111 can be made of the metal oxide with theproportion of oxygen reduced to 90% or less as compared with the laterallayer 112.

That is, the oxygen concentration in the lateral layer 112 is 111% ormore of the oxygen concentration in the resistance change layer 111. Forinstance, in the case where the oxygen concentration in the laterallayer 112 is less than 111% of the oxygen concentration in theresistance change layer 111, the capacity for oxygen supply from thelateral layer 112 to the resistance change layer 111 is lowered, and theeffect described later is decreased.

The resistance change layer 111 and the lateral layer 112 canillustratively be made of an oxide of at least one selected from Si, Ti,Ta, Nb, Hf, Zr, W, Al, Ni, Co, Mn, Fe, Cu, and Mo. Oxide of Al and oxideof Hf are stable and used widely.

On the other hand, the first conductive layer 101 and the secondconductive layer 102 can be made of a material containing an elementwhose “standard free energy of oxide formation” has a smaller absolutevalue than that of the element except oxygen contained in the oxideincluded in the resistance change layer 111. This material can include ametal made of a second element whose “standard free energy of oxideformation” has a smaller absolute value than that of a first elementexcept oxygen contained in the oxide included in the resistance changelayer 111, and an alloy, oxide, nitride, and oxynitride containing thesecond element.

The first conductive layer 101 and the second conductive layer 102 canbe made of a metal such as W, Ta, and Cu, and a metal nitride or carbidesuch as TiN, TaN, and WC.

Furthermore, the first conductive layer 101 and the second conductivelayer 102 can also be made of a semiconductor and the like, such ashighly doped silicon.

FIG. 2 is a schematic view illustrating characteristics of thenonvolatile memory device according to the first embodiment of theinvention.

In FIG. 2, the horizontal axis represents the applied voltage Vapapplied to the resistance change layer 111 (i.e., the potentialdifference between the first conductive layer 101 and the secondconductive layer 102), and the vertical axis represents the current Iflowing in the resistance change layer 111 (i.e., the current flowingbetween the first conductive layer 101 and the second conductive layer102).

As shown in FIG. 2, it is illustratively assumed that the resistancechange layer 111 is in the high-resistance state HRS. If the appliedvoltage Vap is increased in the high-resistance state HRS, then at asecond transition voltage V2 (set voltage), a transition occurs from thehigh-resistance state HRS to the low-resistance state LRS in which theresistance is relatively low. This low-resistance state LRS ismaintained even if the applied voltage Vap is turned off. In thelow-resistance state LRS, if the applied voltage V is increased from 0volts, then at a first transition voltage V1 (reset voltage), atransition to the high-resistance state HRS occurs.

Such a plurality of resistance states in the resistance change layer 111are used for memory operation. The resistance state (memory state) canbe read by applying an applied voltage Vap lower than the firsttransition voltage V1 to the resistance change layer 111.

The transition from the high-resistance state HRS to the low-resistancestate LRS is referred to as set (or set operation), and the transitionfrom the low-resistance state LRS to the high-resistance state HRS isreferred to as reset (or reset operation).

It is noted that multivalued data can also be realized illustratively byestablishing two or more limit current values, and the nonvolatilememory device D101 can also be used as a multivalued memory.

Although FIG. 2 illustrates the characteristics for the case where a DCvoltage is applied to the memory layer 60, a pulse voltage can beapplied to the memory layer 60 to operate the nonvolatile memory deviceD101.

FIGS. 3A and 3B are schematic cross-sectional views illustrating thecharacteristics of the nonvolatile memory device according to the firstembodiment of the invention.

More specifically, FIG. 3A illustrates the reset operation in thenonvolatile memory device D101, and FIG. 3B illustrates the resetoperation for a finer device than in FIG. 3A. In the following example,a description is given of the case where the first conductive layer 101is a cathode and the second conductive layer 102 is an anode.

As shown in FIG. 3A, a filament 111 p is formed in the resistance changelayer 111 illustratively through a forming process. More specifically,for instance, after the memory layer 60 is formed, a voltage (formingvoltage) of a prescribed value or more is applied to the resistancechange layer 111 via the first conductive layer 101 and the secondconductive layer 102 to form a filament 111 p. This filament 111 pserves as a current path in the resistance change layer 111 in thelow-resistance state LRS.

In the reset operation, it is considered that the transition from thelow-resistance state LRS to the high-resistance state HRS occurs by, forinstance, anodic oxidation of the filament 111 p. On the other hand, inthe set operation, it is considered that the transition from thehigh-resistance state HRS to the low-resistance state LRS occurs by, forinstance, reduction of the insulating portion of the oxidized filament111 p.

Here, in the nonvolatile memory device D101, if a voltage higher thanthe first transition voltage V1 is applied in the low-resistance stateLRS, then for instance, in the neighborhood of the second conductivelayer 102 serving as an anode, oxygen 112 o is supplied from the laterallayer 112 to the resistance change layer 111, accelerating oxidation ofthe resistance change layer 111. This facilitates the transition (reset)from the low-resistance state LRS to the high-resistance state HRS inthe resistance change layer 111. Thus, the lateral layer 112 serves tosupply oxygen 112 o to the resistance change layer 111.

Furthermore, as shown in FIG. 3B, even for a fine cell with a reducedcell area (cross-sectional area of the resistance change layer 111 cutalong a plane perpendicular to the stacking direction of the firstconductive layer 101, the resistance change layer 111, and the secondconductive layer 102), the function of the lateral layer 112 forsupplying oxygen 112 o to the resistance change layer 111 is notlowered. The plane perpendicular to the stacking direction maycorrespond to a plane parallel to a substrate on which the nonvolatilememory device is formed. Hence, despite cell downscaling, the transition(reset) from the low-resistance state LRS to the high-resistance stateHRS is easily performed.

In contrast, for instance, in the configuration of a comparative exampleas described in the aforementioned document by Z. Wei et al. in which anoxygen supply layer rich in oxygen is provided on the anode side of theresistance change layer, the volume of the oxygen supply layer decreaseswith the progress of cell downscaling. Hence, in the comparativeexample, particularly when downscaled, it is difficult to supply oxygento the resistance change layer 111 at reset time. Thus, the resetcurrent increases and may destroy, for instance, the driving circuitelement and protection circuit element.

In contrast, in the memory layer 60 of the nonvolatile memory deviceD101 according to this embodiment, the lateral layer 112 being rich inoxygen and having an oxygen supply function is provided on the lateralsurface of the resistance change layer 111. Thus, downscaling of thecell does not result in decreasing the volume of the lateral layer 112.This facilitates resetting and can reduce the reset current and powerconsumption.

Furthermore, the composition of the resistance change layer 111 can bericher in metal than in the case where no lateral layer 112 is provided,and hence the forming voltage can be reduced. Furthermore, as describedlater, depending on the ratio of size (volume) between the resistancechange layer 111 and the lateral layer 112, the forming process can beomitted.

Thus, in the nonvolatile memory device D101, the efficiency of formingcan be improved by reducing the forming voltage or omitting the formingprocess. Hence, a resistance change nonvolatile memory device withreduced reset current can be realized.

Furthermore, in the nonvolatile memory device D101, resetting isfacilitated, and hence the reset operation can be acceleratedsimultaneously.

Furthermore, because of the easy reset operation, the first transitionvoltage V1 (reset voltage) can be reduced. Simultaneously, because ofthe easy reset operation, the filament 111 p is stably insulated, whichrequires a large electric field for the set operation. Consequently, thesecond transition voltage V2 (set voltage) can be kept constant orincreased. This serves to increase the difference between the resetvoltage (e.g., first transition voltage V1) and the set voltage (e.g.,second transition voltage V2), expand the driving margin, and suppressmalfunctions.

It is noted that the width of the lateral layer 112 (the length of thelateral layer 112 in a direction perpendicular to the Z-axis direction)is preferably 1 nm (nanometer) or more from the viewpoint of the amountof oxygen supply from the lateral layer 112 toward the resistance changelayer 111. That is, in the case where the width of the lateral layer 112is smaller (narrower) than 1 nm, the amount of oxygen supply from thelateral layer 112 toward the resistance change layer 111 is small, hencedecreasing the effect of improving the efficiency of forming, such asreduction of the forming voltage, and the effect of reducing the resetcurrent.

FIGS. 4A to 4D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the first embodiment of the invention.

As shown in FIG. 4A, a first conductive film 101 f, which serves as afirst conductive layer 101, is formed illustratively on a substrate 100s. The first conductive film 101 f can be made of the aforementionedmetals and the aforementioned conductive metal compounds, and anyprocess such as the sputtering process, the CVD (chemical vapordeposition) process, and the ALD (atomic layer deposition) process isapplicable thereto.

Next, a resistance change film 111 f to serve as a resistance changelayer 111 is formed. The resistance change film 111 f is made of a metaloxide rich in metal. This film formation can be based on any processsuch as the sputtering process, the CVD process, and the ALD process.For instance, in the case of using the sputtering process, it may bereactive sputtering in which sputtering is performed with oxygenintroduced into the chamber, or oxidation treatment may be performedafter sputtering a metal film. In this case, a desired composition isobtained by controlling, for instance, the oxygen flow rate andoxidation temperature. In the case of using the CVD or ALD process, adesired composition is obtained by controlling, for instance, the filmformation temperature, the flow rate and time of the oxidizer, and theflow rate and time of the metal precursor.

Next, a second conductive film 102 f, which serves as a secondconductive layer 102, is formed. This film formation can also be basedon any process such as the sputtering process, the CVD process, and theALD process.

Here, the aforementioned substrate 100 s can be a semiconductorsubstrate provided with various control circuits and the like. In thecase where a plurality of constituent memory layers including the memorylayer 60 are stacked, the substrate 100 s is made of the constituentmemory layer(s) below the constituent memory layer of interest. Asdescribed later, at least one of the first conductive film 101 f and thesecond conductive film 102 f may be a film serving as at least one of arectifying element, a word line (first wiring), and a bit line (secondwiring). In the following, by way of example, a description is given ofthe case where the first conductive film 101 f and the second conductivefilm 102 f are provided independently of the rectifying element, wordline, and bit line.

Next, as shown in FIG. 4B, a mask 100 r is formed on the secondconductive film 102 f by photolithography, and the second conductivefilm 102 f, the resistance change film 111 f, and the first conductivefilm 101 f are processed illustratively by RIE (reactive ion etching).

Thus, as shown in FIG. 4C, a first conductive layer 101 and a secondconductive layer 102 can be formed, resulting in a configuration inwhich the resistance change film 111 f serving as a resistance changelayer 111 is provided therebetween. That is, the lateral surface of theresistance change film 111 f is formed.

Here, in the case where a plurality of constituent memory layers arevertically stacked, in the vertically adjacent memory layers 60, thelateral surface of the lower memory layer 60 in the X-axis direction andthe lateral surface of one of the word line and the bit line in, forinstance, the X-axis direction can be processed simultaneously with thelateral surface of the upper memory layer 60 in the X-axis direction. Inthe following, a description is given with a focus on only the memorylayer 60.

Then, as shown in FIG. 4D, the lateral surface of the resistance changefilm 111 f is oxidized. More specifically, the resistance change film111 f is annealed in an oxidizing atmosphere to form a lateral layer 112on the lateral surface of the resistance change film 111 f. The centerportion of the resistance change film 111 f constitutes a resistancechange layer 111. The lateral layer 112 having a higher oxygenconcentration than the resistance change layer 111 is formed on thelateral surface of the resistance change layer 111.

In this process, preferably, the first conductive layer 101 and thesecond conductive layer 102 are not oxidized, and the lateral surface ofthe resistance change film 111 f is selectively oxidized. In thisprocess, for instance, it is possible to use thermal oxidation performedin an atmosphere of water and hydrogen at a temperature of 600° C. ormore. It is also possible to use radical oxidation performed in ahydrogen atmosphere at a temperature of 600° C. or more with a traceamount of oxygen added thereto. Furthermore, it is also possible to useplasma oxidation performed in a hydrogen atmosphere at a temperature of600° C. or less with a trace amount of oxygen added thereto.

Furthermore, this process can repair the damage caused to the lateralsurface of the cell in the process of etching the cell described withreference to FIGS. 4B and 4C.

Thus, the nonvolatile memory device D101 illustrated In FIG. 1 can befabricated.

In the nonvolatile memory device D101 according to this embodiment, aclear boundary does not need to exist between the resistance changelayer 111 and the lateral layer 112. That is, in the resistance changelayer, it is only necessary that the oxygen concentration is relativelyhigher on the lateral side than in the center portion in the plane (X-Yplane) perpendicular to the stacking direction (Z-axis direction). Thus,the lateral layer can also be regarded as a portion on the lateral sideof the resistance change layer where the oxygen concentration isrelatively high.

Furthermore, the lateral layer 112 does not necessarily need to beprovided on the lateral surfaces in all directions of the resistancechange layer 111, but only needs to be provided at least part of thelateral surfaces of the resistance change layer 111.

In this example, the lateral layer 112 is also provided between thefirst conductive layer 101 and the second conductive layer 102. However,the lateral layer 112 only needs to be provided on the lateral surfaceof the resistance change layer 111. For instance, part of the laterallayer 112 may be opposed to at least part of the lateral surface of thefirst conductive layer 101 and the lateral surface of the secondconductive layer 102.

Furthermore, at least part of the lateral layer 112 may be providedbetween the first conductive layer 101 and the second conductive layer102.

Furthermore, the lateral layer 112 only needs to function as an oxygensupply layer for the resistance change layer 111. The electricalresistance of the lateral layer 112 may or may not change with at leastone of the electric field applied to and the current passed in thelateral layer 112. That is, the lateral layer 112 is arbitrary in thechange of its electrical resistance.

Thus, the lateral layer 112 functions as an oxygen supply layer for theresistance change layer 111 and has a higher electrical resistance thanthe resistance change layer 111.

Second Embodiment

FIG. 5 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to a secondembodiment of the invention.

As shown in FIG. 5, a memory layer 60 in a nonvolatile memory deviceD102 includes a first conductive layer 101, a second conductive layer102, a resistance change layer 111 (first resistance change layer)provided between the first conductive layer 101 and the secondconductive layer 102, and a lateral layer 113 provided on the lateralsurface of the resistance change layer 111.

The resistance change layer 111 is a layer whose electrical resistancechanges with at least one of the electric field applied thereto and thecurrent passed therein, and can be made of the materials described withreference to the first embodiment. The first and second conductivelayers 101 and 102 can also be made of the materials described withreference to the first embodiment.

The lateral layer 113 is a layer including an oxide of an element whose“standard free energy of oxide formation” has a smaller absolute valuethan that of the element except oxygen contained in the oxide includedin the resistance change layer 111. In the following, for simplicity,the “oxide of an element whose ‘standard free energy of oxide formation’has a smaller absolute value than that of the element except oxygencontained in the oxide included in the resistance change layer” may beabbreviated as “oxide having a lower free energy of formation than theresistance change layer”.

The resistance change layer 111 can illustratively be made of an oxideof Ti, and the lateral layer 113 can illustratively be made of an oxideof Si.

Because Si used in the lateral layer 113 has a smaller absolute value ofthe “standard free energy of oxide formation” than Ti used in theresistance change layer 111, the lateral layer 113 functions as anoxygen supply layer for the resistance change layer 111.

Like the lateral layer 112 in the nonvolatile memory device D101, thelateral layer 113 in the nonvolatile memory device D102 is provided onthe lateral surface of the resistance change layer 111. Thus,downscaling of the cell does not result in decreasing the volume of thelateral layer 113. This facilitates resetting, and can reduce the resetcurrent and power consumption.

Furthermore, because the resistance change layer 111 is easily oxidizedby the lateral layer 113, the resistance change layer 111 can initiallyhave a composition with high conductivity. Consequently, the formingvoltage can be reduced. Furthermore, it is also possible to omit theforming process.

Thus, in the nonvolatile memory device D102, the efficiency of formingis improved by reducing the forming voltage or omitting the formingprocess. Hence, a resistance change nonvolatile memory device withreduced reset current can be realized.

Furthermore, in the nonvolatile memory device D102, as in thenonvolatile memory device D101, the reset operation can be accelerated,the difference between the reset voltage and the set voltage can beincreased, and malfunctions can be suppressed.

In this embodiment, it is only necessary that the lateral layer 113includes an oxide having a lower free energy of formation than theresistance change layer 111. The resistance change layer 111 and thelateral layer 113 are not limited to binary compounds, but may be madeof ternary or higher compounds.

The absolute value of the “standard free energy of oxide formation” ofthe element except oxygen in the oxide included in the lateral layer 113(the element except oxygen contained in the oxide) is set smaller thanthe absolute value of the “standard free energy of oxide formation” ofthe element except oxygen in the oxide included in the resistance changelayer 111. Here, if the difference between these values (these absolutevalues) increases, the effect of supplying oxygen from the lateral layer113 to the resistance change layer 111 is enhanced, which furtherfacilitates resetting, and consequently increases the effect of reducingthe forming voltage. On the other hand, if the difference between thesevalues is small, the degree of facilitating resetting is relativelysmall, whereas setting becomes easier.

Thus, while the absolute value of the “standard free energy of oxideformation” of the element except oxygen in the oxide included in thelateral layer 113 is set smaller than the absolute value of the“standard free energy of oxide formation” of the element except oxygenin the oxide included in the resistance change layer 111, the differencebetween these values can be suitably adapted to desired characteristics.

In the foregoing description, the reset operation and the set operationare performed on the basis of the reduction and oxidation of thefilament 111 p, for instance, serving as a current path of theresistance change layer 111. However, the set operation may be performedon the basis of the electric field applied to the resistance changelayer 111. In this case, the difference between the absolute value ofthe “standard free energy of oxide formation” of the element exceptoxygen in the oxide included in the lateral layer 113 and the absolutevalue of the “standard free energy of oxide formation” of the elementexcept oxygen in the oxide included in the resistance change layer 111is preferably increased so that the reset operation can be facilitatedwithout substantially exerting an adverse effect on the set operation.

FIGS. 6A to 6D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the second embodiment of the invention.

The process from FIG. 6A to FIG. 6C is similar to that for thenonvolatile memory device D101, and hence the description thereof isomitted.

After the first conductive layer 101, the second conductive layer 102,and the resistance change layer 111 are formed, as shown in FIG. 6D, asilicon oxide film, for instance, which serves as a lateral layer 113having the function of an oxygen supply layer, is formed on the lateralsurfaces and upper surfaces of the first conductive layer 101, thesecond conductive layer 102, and the resistance change layer 111. Thisfilm formation can illustratively be based on the ALD film formation ata low temperature of 400° C. or less using 3DMAS(tris(dimethylamino)silane) and ozone. In this case, a film capable ofeasily supplying oxygen can be formed illustratively by using acondition in which the proportion of 3DMAS is decreased and ozone isincreased as compared with the film formation condition for a siliconoxide film serving as an interlayer insulating film.

The lateral layer 113 is preferably made of a silicon oxide film, whicheasily supplies oxygen. Specifically, it is possible to choose a filmwith the composition ratio of oxygen to silicon being approximately 2 ormore.

The width of the lateral layer 113 (the length of the lateral layer 113in a direction perpendicular to the Z-axis direction) is preferably 1 nmor more from the viewpoint of the amount of oxygen supply from thelateral layer 113 toward the resistance change layer 111. That is, inthe case where the width of the lateral layer 113 is smaller than 1 nm,the amount of oxygen supply from the lateral layer 113 toward theresistance change layer 111 is small, hence decreasing the effect suchas reduction of the forming voltage, and the effect of reducing thereset current.

In the nonvolatile memory device D102, a clear boundary does not need toexist between the resistance change layer 111 and the lateral layer 113.That is, in the resistance change layer, the content of the elementwhose “standard free energy of oxide formation” has a relatively smallabsolute value (the element except oxygen) may be higher on the lateralside than in the center portion in the plane (X-Y plane) perpendicularto the stacking direction (Z-axis direction). For instance, the centerportion of the resistance change layer may be substantially made of anoxide of Ti, in which from the center portion toward the lateralsurface, the content of Ti decreases, whereas the content of Siconversely increases. Thus, the lateral layer can also be regarded as aportion on the lateral side of the resistance change layer where theconcentration of the element whose “standard free energy of oxideformation” has a small absolute value is relatively higher than in thecenter portion.

Furthermore, the lateral layer 113 does not necessarily need to beprovided on the lateral surfaces in all directions of the resistancechange layer 111, but only needs to be provided at least part of thelateral surfaces of the resistance change layer 111.

Furthermore, the lateral layer 113 only needs to function as an oxygensupply layer for the resistance change layer 111. The electricalresistance of the lateral layer 113 may or may not change with at leastone of the electric field applied to and the current passed in thelateral layer 113. That is, the lateral layer 113 is arbitrary in thechange of its electrical resistance.

Thus, the lateral layer 113 functions as an oxygen supply layer for theresistance change layer 111 and has a higher electrical resistance thanthe resistance change layer 111.

FIG. 7 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to thesecond embodiment of the invention.

As shown in FIG. 7, in a nonvolatile memory device D103 of a variationaccording to this embodiment, part of a lateral layer 114 is providedbetween the first conductive layer 101 and the second conductive layer102. Furthermore, another part of the lateral layer 114 is opposed tothe lateral surface of the first conductive layer 101 and the lateralsurface of the second conductive layer 102.

Thus, the lateral layer 114 only needs to be provided on the lateralsurface of the resistance change layer 111. For instance, at least partof the lateral layer 114 may be provided between the first conductivelayer 101 and the second conductive layer 102.

Like the aforementioned lateral layer 113, the lateral layer 114 is alayer including an oxide of an element whose “standard free energy ofoxide formation” has a smaller absolute value than that of the elementexcept oxygen contained in the oxide included in the resistance changelayer 111. Thus, the nonvolatile memory device D103 has an effectsimilar to that of the nonvolatile memory device D102.

As described earlier, also in the nonvolatile memory device D101according to the first embodiment, like the lateral layer 114illustrated in FIG. 7, part of the lateral layer 112 may be opposed toat least part of the lateral surface of the first conductive layer 101and the lateral surface of the second conductive layer 102. Furthermore,at least part of the lateral layer 112 may be provided between the firstconductive layer 101 and the second conductive layer 102. Also in thiscase, an effect similar to that of the nonvolatile memory device D101 isachieved.

Third Embodiment

FIGS. 8A to 8C are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a thirdembodiment of the invention.

As shown in FIG. 8A, a nonvolatile memory device D104 according to thisembodiment includes a first conductive layer 101, a second conductivelayer 102, a first resistance change layer 111 provided between thefirst conductive layer 101 and the second conductive layer 102 andhaving an electrical resistance changing with at least one of theelectric field applied thereto and the current passed therein, and afirst lateral layer 112 provided on the lateral surface of the firstresistance change layer 111 and having a higher oxygen concentrationthan the first resistance change layer 111.

The nonvolatile memory device D104 further includes a third conductivelayer 103 opposed to the lateral surface of the first conductive layer101, a fourth conductive layer 104 opposed to the lateral surface of thesecond conductive layer 102, a second resistance change layer 111 aprovided between the third conductive layer 103 and the fourthconductive layer 104 and having an electrical resistance changing withat least one of the electric field applied thereto and the currentpassed therein, a second lateral layer 112 a provided on the lateralsurface of the second resistance change layer 111 a on the first laterallayer 112 side, and an interlayer insulating film 120 provided betweenthe first lateral layer 112 and the second lateral layer 112 a.

The second lateral layer 112 a is made of a compound having a higheroxygen concentration than the second resistance change layer 111 a. Forinstance, the second resistance change layer 111 a can be made of amaterial similar to that of the first resistance change layer 111, andthe second lateral layer 112 a can be made of a material similar to thatof the first lateral layer 112.

More specifically, for instance, the first and second resistance changelayers 111 and 111 a can be made of an oxide of a transition metal, andthe first and second lateral layers 112 and 112 a can be made of anoxide of the transition metal included in the first and secondresistance change layers 111 and 111 a and having a higher oxygenconcentration than the first and second resistance change layers 111 and111 a.

The interlayer insulating film 120 can be made of a compound having ahigher oxygen concentration than the first lateral layer 112 and thesecond lateral layer 112 a.

More specifically, in this case, the interlayer insulating film 120 hasa higher oxygen concentration than the first and second resistancechange layers 111 and 111 a and also has a higher oxygen concentrationthan the first and second lateral layers 112 and 112 a. This allowsoxygen contained in the first and second lateral layers 112 and 112 a toeasily migrate toward the first and second resistance change layers 111and 111 a rather than toward the interlayer insulating film 120. Thisfurther enhances the capacity for oxygen supply of the first laterallayer 112 and the second lateral layer 112 a to the first resistancechange layer 111 and the second resistance change layer 111 a.

Alternatively, the interlayer insulating film 120 may have a loweroxygen concentration than the first and second lateral layers 112 and112 a. For instance, the oxygen concentration in the interlayerinsulating film 120 can be optimized from the viewpoint of insulationperformance of the interlayer insulating film 120. Here, even if theoxygen concentration in the interlayer insulating film 120 is lower thanthat in the first and second lateral layers 112 and 112 a, the oxygenconcentration in the first and second lateral layers 112 and 112 a ishigher than that in the first and second resistance change layers 111and 111 a. This allows oxygen in the first and second lateral layers 112and 112 a to easily migrate toward the first and second resistancechange layers 111 and 111 a. That is, while imparting high insulationperformance to the interlayer insulating film 120, it is possible toprovide the first and second lateral layers 112 and 112 a functioning asoxygen supply layers.

Furthermore, in the nonvolatile memory device D104, the interlayerinsulating film 120 can illustratively include an oxide of an elementwhose “standard free energy of oxide formation” has a smaller absolutevalue than that of the element except oxygen in the oxide included inthe first lateral layer 112 and the second lateral layer 112 a. Thisallows oxygen contained in the first and second lateral layers 112 and112 a to easily migrate toward the first and second resistance changelayers 111 and 111 a rather than toward the interlayer insulating film120.

As shown in FIG. 8B, a nonvolatile memory device D105 according to thisembodiment includes a first conductive layer 101, a second conductivelayer 102, a first resistance change layer 111, and a first laterallayer 113 provided on the lateral surface of the first resistance changelayer 111 and including an oxide of an element whose “standard freeenergy of oxide formation” has a smaller absolute value than that of theelement except oxygen in the oxide included in the first resistancechange layer 111.

The nonvolatile memory device D105 further includes a third conductivelayer 103, a fourth conductive layer 104, a second resistance changelayer 111 a, a second lateral layer 113 a provided on the lateralsurface of the second resistance change layer 111 a on the first laterallayer 113 side, and an interlayer insulating film 120 provided betweenthe first lateral layer 113 and the second lateral layer 113 a.

The second lateral layer 113 a includes an oxide of an element whose“standard free energy of oxide formation” has a smaller absolute valuethan that of the element except oxygen in the oxide included in thesecond resistance change layer 111 a.

Furthermore, the interlayer insulating film 120 can include an oxide ofan element whose “standard free energy of oxide formation” has a smallerabsolute value than that of the element except oxygen in the oxideincluded in the first lateral layer 113 and the second lateral layer 113a.

That is, the nonvolatile memory device D105 is made of oxides of anelement with the absolute value of the “standard free energy of oxideformation” decreasing in the order of the first and second resistancechange layers 111 and 111 a, the first and second lateral layers 113 and113 a, and the interlayer insulating film 120.

This allows oxygen contained in the first and second lateral layers 113and 113 a to easily migrate toward the first and second resistancechange layers 111 and 111 a rather than toward the interlayer insulatingfilm 120.

Furthermore, in the nonvolatile memory device D105, the interlayerinsulating film 120 can be made of a compound having a lower oxygenconcentration than the first lateral layer 113 and the second laterallayer 113 a.

More specifically, for instance, the first and second resistance changelayers 111 and 111 a can be made of an oxide of Ti, the first and secondlateral layers 113 and 113 a can be made of a compound of Si (SiO_(2+δ),where δ is positive) having a relatively high oxygen concentration, andthe interlayer insulating film 120 can be made of a compound of Si(SiO₂) having a relatively low oxygen concentration. Hence, whilemaintaining high insulation performance in the interlayer insulatingfilm 120, it is possible to relatively increase the oxygen concentrationin the first and second lateral layers 113 and 113 a. This allows oxygencontained in the first and second lateral layers 113 and 113 a to easilymigrate toward the first and second resistance change layers 111 and 111a. This facilitates forming of the first and second resistance changelayers 111 and 111 a, improves the efficiency of forming by reducing theforming voltage or omitting the forming process, and can reduce thereset current.

As shown in FIG. 8C, in a nonvolatile memory device D106 according tothis embodiment, a first lateral layer 114 and a second lateral layer114 a are opposed to the lateral surfaces of a first conductive layer101 and a second conductive layer 102 and the lateral surfaces of athird conductive layer 103 and a fourth conductive layer 104,respectively. Part of the first lateral layer 114 and part of the secondlateral layer 114 a are sandwiched between the first conductive layer101 and the second conductive layer 102 and between the third conductivelayer 103 and the fourth conductive layer 104, respectively. The firstlateral layer 114 and the second lateral layer 114 a can each be basedon at least one of the configuration of the first lateral layer 112 andthe second lateral layer 112 a and the configuration of the firstlateral layer 113 and the second lateral layer 113 a described above.

In the embodiments of the invention, the lateral layer 112 (firstlateral layer 112 and second lateral layer 112 a) having a higher oxygenconcentration than the resistance change layer 111 (first resistancechange layer 111 and second resistance change layer 111 a) may beprovided simultaneously with the lateral layer 113 (first lateral layer113 and second lateral layer 113 a) including an oxide having a lowerfree energy of formation than the resistance change layer 111 (firstresistance change layer 111 and second resistance change layer 111 a).

Fourth Embodiment

In a fourth embodiment of the invention, in addition to at least one ofthe lateral layer 112 and the lateral layer 113 described above, atleast one of a layer having a higher oxygen concentration than theresistance change layer 111 and a layer including an oxide having alower free energy of formation than the resistance change layer 111 isfurther provided between the resistance change layer 111 and at leastone of the first conductive layer 101 and the second conductive layer102.

FIGS. 9A to 9F are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to the fourthembodiment of the invention.

As shown in FIG. 9A, in a nonvolatile memory device D111 according tothis embodiment, in addition to a lateral layer 112, a layer 112 uhaving a higher oxygen concentration than a resistance change layer 111is further provided between the resistance change layer 111 and a secondconductive layer 102 (e.g., anode).

Here, in addition to the lateral layer 112, a layer having a higheroxygen concentration than the resistance change layer 111 may be furtherprovided between the resistance change layer 111 and a first conductivelayer 101 (e.g., cathode).

As shown in FIG. 9B, in a nonvolatile memory device D112 according tothis embodiment, in addition to a lateral layer 112, layers 112 d and112 u having a higher oxygen concentration than a resistance changelayer 111 are further provided between the resistance change layer 111on the one hand and a first conductive layer 101 and a second conductivelayer 102 on the other, respectively.

As shown in FIG. 9C, in a nonvolatile memory device D113 according tothis embodiment, in addition to a lateral layer 113, a layer 112 uhaving a higher oxygen concentration than a resistance change layer 111is further provided between the resistance change layer 111 and a secondconductive layer 102.

Here, in addition to the lateral layer 113, a layer having a higheroxygen concentration than the resistance change layer 111 may be furtherprovided between the resistance change layer 111 and a first conductivelayer 101.

As shown in FIG. 9D, in a nonvolatile memory device D114 according tothis embodiment, in addition to a lateral layer 113, layers 112 d and112 u having a higher oxygen concentration than a resistance changelayer 111 are further provided between the resistance change layer 111on the one hand and a first conductive layer 101 and a second conductivelayer 102 on the other, respectively.

As shown in FIG. 9E, in a nonvolatile memory device D115 according tothis embodiment, in addition to a lateral layer 112, a layer 112 uhaving a higher oxygen concentration than a resistance change layer 111is provided between the resistance change layer 111 and a secondconductive layer 102. Furthermore, a lateral layer 113 including anoxide having a lower free energy of formation than the resistance changelayer 111 is provided on the lateral surface of the lateral layer 112.Here, in addition to the lateral layer 112, a layer having a higheroxygen concentration than the resistance change layer 111 may beprovided between the resistance change layer 111 and a first conductivelayer 101, and the lateral layer 113 may be further provided on thelateral surface of the lateral layer 112.

As shown in FIG. 9F, in a nonvolatile memory device D116 according tothis embodiment, in addition to a lateral layer 112, layers 112 d and112 u having a higher oxygen concentration than a resistance changelayer 111 are further provided between the resistance change layer 111on the one hand and a first conductive layer 101 and a second conductivelayer 102 on the other, respectively. Furthermore, a lateral layer 113including an oxide having a lower free energy of formation than theresistance change layer 111 is provided on the lateral surface of thelateral layer 112.

FIGS. 10A to 10F are schematic cross-sectional views illustrating theconfigurations of other nonvolatile memory devices according to thefourth embodiment of the invention.

As shown in FIG. 10A, in a nonvolatile memory device D121 according tothis embodiment, in addition to a lateral layer 112, a layer 113 uincluding an oxide having a lower free energy of formation than aresistance change layer 111 is further provided between the resistancechange layer 111 and a second conductive layer 102 (e.g., anode).

Here, in addition to the lateral layer 112, a layer including an oxidehaving a lower free energy of formation than the resistance change layer111 may be further provided between the resistance change layer 111 anda first conductive layer 101 (e.g., cathode).

As shown in FIG. 10B, in a nonvolatile memory device D122 according tothis embodiment, in addition to a lateral layer 112, layers 113 d and113 u including an oxide having a lower free energy of formation thanthe resistance change layer 111 are further provided between aresistance change layer 111 on the one hand and a first conductive layer101 and a second conductive layer 102 on the other, respectively.

As shown in FIG. 10C, in a nonvolatile memory device D123 according tothis embodiment, in addition to a lateral layer 113, a layer 113 uincluding an oxide having a lower free energy of formation than aresistance change layer 111 is further provided between the resistancechange layer 111 and a second conductive layer 102.

Here, in addition to the lateral layer 113, a layer including an oxidehaving a lower free energy of formation than the resistance change layer111 may be further provided between the resistance change layer 111 anda first conductive layer 101.

As shown in FIG. 10D, in a nonvolatile memory device D124 according tothis embodiment, in addition to a lateral layer 113, layers 113 d and113 u including an oxide having a lower free energy of formation than aresistance change layer 111 are further provided between the resistancechange layer 111 on the one hand and a first conductive layer 101 and asecond conductive layer 102 on the other, respectively.

As shown in FIG. 10E, in a nonvolatile memory device D125 according tothis embodiment, in addition to a lateral layer 112, a layer 113 uincluding an oxide having a lower free energy of formation than aresistance change layer 111 is provided between the resistance changelayer 111 and a second conductive layer 102. Furthermore, a laterallayer 113 including an oxide having a lower free energy of formationthan the resistance change layer 111 is provided on the lateral surfaceof the lateral layer 112.

Here, in addition to the lateral layer 112, a layer including an oxidehaving a lower free energy of formation than the resistance change layer111 may be provided between the resistance change layer 111 and a firstconductive layer 101, and the lateral layer 113 may be further providedon the lateral surface of the lateral layer 112.

As shown in FIG. 10F, in a nonvolatile memory device D126 according tothis embodiment, in addition to a lateral layer 112, layers 113 d and113 u including an oxide having a lower free energy of formation than aresistance change layer 111 are further provided between the resistancechange layer 111 on the one hand and a first conductive layer 101 and asecond conductive layer 102 on the other, respectively. Furthermore, alateral layer 113 including an oxide having a lower free energy offormation than the resistance change layer 111 is provided on thelateral surface of the lateral layer 112.

Thus, various modifications are applicable to the nonvolatile memorydevice according to this embodiment. Also in these nonvolatile memorydevices, the forming voltage can be reduced, the efficiency of formingcan be improved, and the reset current can be reduced.

More specifically, in various nonvolatile memory devices according tothis embodiment, a layer serving as an oxygen supply layer (laterallayers 112 and 113) is provided on the lateral surface of the resistancechange layer 111, and also provided on the surface located in the filmthickness direction of the resistance change layer 111. Hence, asdescribed with reference to the first to third embodiments, even for afine cell, resetting can be easily performed. Furthermore, because theoxygen supply layer is provided also near the anode and cathode,resetting can be performed more easily than in the first to thirdembodiments. Furthermore, because the resistance change layer 111 havinga metal-rich composition is provided in the center portion between thefirst conductive layer 101 and the second conductive layer 102, theforming voltage can be reduced.

FIGS. 11A to 11E are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the fourth embodiment of the invention.

More specifically, FIGS. 11A to 11E illustrate a method formanufacturing the nonvolatile memory device D116 illustrated in FIG. 9F.

First, as shown in FIG. 11A, a first conductive film 101 f, which servesas a first conductive layer 101, is formed on a substrate 100 s. Then, afilm 112 df, which serves as a layer 112 d having an oxygen-richcomposition, is formed thereon. For instance, in the case of using thesputtering process, the oxygen flow rate and the oxidation temperatureare made higher than in the film formation of the resistance change film111 f (a relatively metal-rich film) described later. In the case ofusing the ALD or CVD process, film formation is performed by increasingthe flow rate and time of the oxidizer and decreasing the flow rate andtime of the metal precursor as compared with the film formation of theresistance change film 111 f.

Subsequently, a resistance change film 111 f, which serves as aresistance change layer 111, is formed. This can be based on the methoddescribed with reference to the first embodiment.

Subsequently, by a method similar to that for the film 112 df, forinstance, a film 112 uf, which serves as a layer 112 u having anoxygen-rich composition, is formed on the resistance change film 111 f.

Then, a second conductive film 102 f is formed thereon.

Subsequently, as shown in FIGS. 11B and 11C, for instance, by the methoddescribed in the first embodiment, the second conductive film 102 f, thefilm 112 uf, the resistance change film 111 f, the film 112 df, and thefirst conductive film 101 f are processed. Thus, a first conductivelayer 101, a layer 112 d, a layer 112 u, and a second conductive layer102 are formed, and the resistance change film 111 f serving as aresistance change layer 111 is formed therebetween. That is, the lateralsurface of the resistance change film 111 f is formed.

Then, as shown in FIG. 11D, for instance, by the method described in thefirst embodiment, the lateral surface of the resistance change film 111f is oxidized to form a lateral layer 112. Simultaneously, the damagecaused to the lateral surface of the cell in the etching process isrepaired.

Then, as shown in FIG. 11E, for instance, by the method described withrespect to the second embodiment, a silicon oxide film, for instance,which serves as a lateral layer 113 functioning as an oxygen supplylayer is formed. Then, the silicon oxide film on the second conductivelayer 102 is removed as necessary, and an interlayer insulating film isformed.

Thus, the nonvolatile memory device D116 can be fabricated.

It is noted that various nonvolatile memory devices and the variationsthereof illustrated in FIGS. 9A to 9E and FIGS. 10A to 10F can also befabricated by using methods similar to the foregoing, suitably modifiedif necessary.

Fifth Embodiment

FIGS. 12A to 12F are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a fifthembodiment of the invention.

As shown in FIG. 12A, a nonvolatile memory device D131 according to thisembodiment further includes a diffusion barrier layer 115 providedbetween a resistance change layer 111 and a lateral layer 112. Thelateral layer 112 is a layer having a higher oxygen concentration thanthe resistance change layer 111. In the following, for simplicity, the“layer having a higher oxygen concentration than the resistance changelayer” is simply referred to as the “layer having high oxygenconcentration”.

As shown in FIG. 12B, another nonvolatile memory device D132 accordingto this embodiment further includes a diffusion barrier layer 115provided between a resistance change layer 111 and a lateral layer 113(the layer including an oxide having a lower free energy of formationthan the resistance change layer 111).

As shown in FIG. 12C, another nonvolatile memory device D133 accordingto this embodiment further includes, besides a lateral layer 112, alayer 112 u having high oxygen concentration provided between aresistance change layer 111 and a second conductive layer 102, and adiffusion barrier layer 115 provided between the resistance change layer111 and the layer 112 u.

Here, besides the lateral layer 112, a layer 112 d having high oxygenconcentration may be provided between the resistance change layer 111and a first conductive layer 101, and the diffusion barrier layer 115may be further provided between the resistance change layer 111 and thelayer 112 d.

As shown in FIG. 12D, a nonvolatile memory device D134 according to thisembodiment further includes, besides a lateral layer 113, a layer 112 uhaving high oxygen concentration provided between a resistance changelayer 111 and a second conductive layer 102, and a diffusion barrierlayer 115 provided between the resistance change layer 111 and the layer112 u.

Here, besides the lateral layer 113, a layer 112 d having high oxygenconcentration may be provided between the resistance change layer 111and a first conductive layer 101, and the diffusion barrier layer 115may be further provided between the resistance change layer 111 and thelayer 112 d.

As shown in FIG. 12E, a nonvolatile memory device D135 according to thisembodiment further includes, besides a lateral layer 112, a layer 113 uprovided between a resistance change layer 111 and a second conductivelayer 102 and including an oxide having a lower free energy of formationthan the resistance change layer 111, and a diffusion barrier layer 115provided between the resistance change layer 111 and the layer 113 u.

Here, besides the lateral layer 112, a layer 113 d including an oxidehaving a lower free energy of formation than the resistance change layer111 may be provided between the resistance change layer 111 and a firstconductive layer 101, and the diffusion barrier layer 115 may be furtherprovided between the resistance change layer 111 and the layer 113 d.

As shown in FIG. 12F, a nonvolatile memory device D136 according to thisembodiment further includes, besides a lateral layer 113, a layer 113 uprovided between a resistance change layer 111 and a second conductivelayer 102 and including an oxide having a lower free energy of formationthan the resistance change layer 111, and a diffusion barrier layer 115provided between the resistance change layer 111 and the layer 113 u.

Here, besides the lateral layer 113, a layer 113 d including an oxidehaving a lower free energy of formation than the resistance change layer111 may be provided between the resistance change layer 111 and a firstconductive layer 101, and the diffusion barrier layer 115 may be furtherprovided between the resistance change layer 111 and the layer 113 d.

The diffusion barrier layer 115 illustrated in FIGS. 12A and 12B has theeffect of suppressing migration of metallic elements in at least one ofbetween the resistance change layer 111 and the lateral layer 112 andbetween the resistance change layer 111 and the lateral layer 113.

The diffusion barrier layer 115 illustrated in FIGS. 12C to 12F has theeffect of suppressing migration of metallic elements in at least one ofbetween the resistance change layer 111 and at least one of the layers112 u and 112 d and between the resistance change layer 111 and at leastone of the layers 113 u and 113 d.

That is, the diffusion barrier layer 115 is a layer in which the elementexcept oxygen contained in the resistance change layer 111 migrates lesseasily than in the resistance change layer 111.

The diffusion barrier layer 115 can suppress diffusion of metals by heatapplied to the resistance change film 111 f (resistance change layer111) in various processes for manufacturing the nonvolatile memorydevice. Thus, a nonvolatile memory device further fitted to desiredcharacteristics can be fabricated.

The diffusion barrier layer 115 can illustratively be made of siliconnitride film, silicon oxide film, and nitrides obtained by, forinstance, nitridizing the metal oxide included in the resistance changelayer 111. For instance, in the case where the resistance change layer111 is made of HfO₂, the diffusion barrier layer 115 can be made of amaterial (HfN_(x) and HfON) obtained by nitridizing HfO₂. Then, thediffusion constant of Hf in the diffusion barrier layer 115 (HfN_(x) andHfON) is smaller than ease of migration of Hf in the resistance changelayer 111 (HfO₂). This can suppress diffusion of Hf between theresistance change layer 111 and various layers opposed thereto (laterallayers 112 and 113, and layers 112 u, 112 d, 113 u, and 113 d),achieving stable characteristics.

It is noted that thermal stress in the process for manufacturing thenonvolatile memory device is e.g. approximately 750 to 800° C. or less.The diffusion barrier layer 115 can be designed to suppress diffusion ofmetals under this condition.

It is noted that during operation of the completed nonvolatile memorydevice, the resistance change layer 111 is heated by, for instance, atleast one of the electric field applied thereto and the current passedtherein. However, this heating is more local than heating in themanufacturing process, and its time is shorter. The diffusion barrierlayer 115 is designed so as to substantially avoid disturbing themigration of oxygen between the resistance change layer 111 and at leastone of the lateral layer 112 and the lateral layer 113 while alsosuppressing diffusion of metals at the temperature during thisoperation. Furthermore, in the case where the layers 112 u, 112 d, 113u, and 113 d are provided, the diffusion barrier layer 115 is designedso as to substantially avoid disturbing the migration of oxygen betweenthe resistance change layer 111 and these layers while also suppressingdiffusion of metals at the temperature during this operation.

The configurations illustrated in FIGS. 12A to 12F are some of theexample configurations of the diffusion barrier layer 115, and variousmodifications are applicable to the layout of the diffusion barrierlayer 115.

More specifically, the diffusion barrier layer 115 in which the elementexcept oxygen contained in the resistance change layer 111 has a lowerdiffusion constant than in the resistance change layer 111 can beprovided in at least one of at least in part between the resistancechange layer 111 and the lateral layer 112, and at least in part betweenthe resistance change layer 111 and the lateral layer 113.

Furthermore, in the case where the layer 112 d having a higher oxygenconcentration than the resistance change layer 111 is provided betweenthe resistance change layer 111 and the first conductive layer 101, theaforementioned diffusion barrier layer 115 can be provided at least inpart between the resistance change layer 111 and the layer 112 d. Here,in the case where the layer 112 u having a higher oxygen concentrationthan the resistance change layer 111 is further provided between theresistance change layer 111 and the second conductive layer 102, theaforementioned diffusion barrier layer 115 can be provided in at leastpart of at least in part between the resistance change layer 111 and thelayer 112 d and at least in part between the resistance change layer 111and the layer 112 u.

Furthermore, in the case where the layer 113 d including an oxide havinga lower free energy of formation than the resistance change layer 111 isprovided between the resistance change layer 111 and the firstconductive layer 101, the aforementioned diffusion barrier layer 115 canbe provided at least in part between the resistance change layer 111 andthe layer 113 d. Here, in the case where the layer 113 u including anoxide having a lower free energy of formation than the resistance changelayer 111 is further provided between the resistance change layer 111and the second conductive layer 102, the aforementioned diffusionbarrier layer 115 can be provided in at least part of at least in partbetween the resistance change layer 111 and the layer 113 d and at leastin part between the resistance change layer 111 and the layer 113 u.

FIGS. 13A to 13F are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing another nonvolatilememory device according to the fifth embodiment of the invention.

First, as shown in FIG. 13A, a first conductive film 101 f, which servesas a first conductive layer 101, is formed on a substrate 100 s. Then, afilm 112 df, which serves as a layer 112 d having an oxygen-richcomposition, is formed thereon.

Subsequently, a film 115 df, which serves as a diffusion barrier layer115 d, is formed. For instance, in the case where the diffusion barrierlayer 115 d is made of silicon oxide film, the film 115 df can be formedby the ALD process using 3DMAS and ozone at a temperature ofapproximately 500° C. Alternatively, the film 115 df may be formed bythe CVD process using dichlorosilane and nitrous oxide at a hightemperature of approximately 700° C. In the case where the diffusionbarrier layer 115 d is made of silicon nitride film, the film 115 df canbe formed using dichlorosilane and ammonia by the ALD process at atemperature of approximately 400° C., or by the CVD process at atemperature of approximately 700° C. In the case where the film 115 dfis formed by nitridizing the film 112 df, the film 112 df may bethermally nitridized using ammonia at a temperature of e.g.approximately 800° C., or may be subjected to plasma nitridation using anitrogen plasma.

Subsequently, a resistance change film 111 f, which serves as aresistance change layer 111, is formed. This can be based on the methoddescribed with reference to the first embodiment.

Subsequently, a film 115 uf, which serves as a diffusion barrier layer115 u, is formed on the resistance change film 111 f. The film formationof the film 115 uf can illustratively be based on technically applicablemethods of those described with reference to the film 115 df.

Subsequently, by a method similar to that for the film 112 df, forinstance, a film 112 uf, which serves as a layer 112 u having anoxygen-rich composition, is formed.

Then, a second conductive film 102 f is formed thereon.

Subsequently, as shown in FIGS. 13B and 13C, for instance, by the methoddescribed in the first embodiment, the second conductive film 102 f, thefilm 112 uf, the film 115 uf, the resistance change film 111 f, the film112 df, the film 115 df, and the first conductive film 101 f areprocessed to form a first conductive layer 101 and a second conductivelayer 102. Then, the lateral surface of the resistance change film 111 fis formed.

Then, as shown in FIG. 13D, the lateral portions of the film 112 uf, theresistance change film 111 f, and the film 112 df are nitridized to forma film 115 sf serving as a diffusion barrier layer 115 s on the lateralsurface of the stacked structure of the film 112 uf, the resistancechange film 111 f, and the film 112 df.

Then, as shown in FIG. 13E, the surface (sidewall surface) of the film115 sf is oxidized to form a lateral layer 112 having high oxygenconcentration.

Then, as shown in FIG. 13F, a layer 113 including an oxide having alower free energy of formation than the resistance change layer 111 isformed on the lateral surfaces of the first conductive layer 101, thelateral layer 112, and the second conductive layer 102.

Thus, the nonvolatile memory device D137 illustrated in FIG. 13F can befabricated.

In the nonvolatile memory device D137, the lateral layer 112 and thelateral layer 113 are provided on the lateral surface of the resistancechange layer 111. Thus, the forming voltage can be reduced, theefficiency of forming can be improved, and the reset current can bereduced. Furthermore, the layers 112 d and 112 u having high oxygenconcentration are provided between the resistance change layer 111 onthe one hand and the first conductive layer 101 and the secondconductive layer 102 on the other, respectively. Hence, the resetoperation is further facilitated. Furthermore, the diffusion barrierlayer 115 s is provided between the resistance change layer 111 and thelateral layer 112, and the diffusion barrier layers 115 d and 115 u areprovided between the resistance change layer 111 on the one hand and thelayers 112 d and 112 u on the other, respectively. This can suppress,for instance, diffusion of the element except oxygen contained in theresistance change layer 111 by application of heat during themanufacturing process, achieving more stable operation.

Sixth Embodiment

FIGS. 14A and 14B are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a sixthembodiment of the invention.

As shown in FIG. 14A, in a nonvolatile memory device D141 according tothis embodiment, the cross section of a resistance change layer 111 cutalong a plane (X-Y plane) perpendicular to the Z-axis direction (thestacking direction of a first conductive layer 101, the resistancechange layer 111, and a second conductive layer 102) is smaller on thesecond conductive layer 102 (e.g., anode) side than in the centerportion between the first conductive layer 101 and the second conductivelayer 102.

That is, the lateral surface of the resistance change layer 111 on thesecond conductive layer 102 side is set back relative to the centerportion.

Thus, at reset time, an electric field is efficiently applied to theresistance change layer 111 near the second conductive layer 102, andoxygen is collected more easily from a lateral layer 112 on the secondconductive layer 102 side of the resistance change layer 111, whichfurther facilitates the reset operation.

As shown in FIG. 14B, in a nonvolatile memory device D142 according tothis embodiment, the cross section of a resistance change layer 111 cutalong the X-Y plane is smaller on the side of a first conductive layer101 and a second conductive layer 102 than in the center portion betweenthe first conductive layer 101 and the second conductive layer 102.

That is, the lateral surface of the resistance change layer 111 on theside of the first and second conductive layers 101 and 102 is set backrelative to the center portion.

In this case, at reset time, in the aforementioned cross section of theresistance change layer 111, a filament 111 p is formed more easily inthe center portion, but less easily in the end portion of the resistancechange layer 111. This can suppress destruction of the cell due toelectric field concentration on the end portion of the resistance changelayer 111. Furthermore, it is also possible to suppress characteristicsvariation between cells due to formation of the filament 111 p at theend portion.

It is noted that as described above, in the nonvolatile memory deviceaccording to the embodiments of the invention, the first conductivelayer 101 and the second conductive layer 102 are interchangeable.

More specifically, in this embodiment, the cross section of theresistance change layer 111 cut along a plane perpendicular to thestacking direction of the first conductive layer 101, the resistancechange layer 111, and the second conductive layer 102 is designed to besmaller on at least one side of the first and second conductive layers101 and 102 than in the center portion between the first conductivelayer 101 and the second conductive layer 102.

For instance, the cross section of the resistance change layer 111 (thecross section along the X-Y plane) on the first conductive layer 101side, rather than on the second conductive layer 102 side, may besmaller than in the center portion.

Here, in the case where the cross section of the resistance change layer111 is smaller on one side of the first conductive layer 101 and thesecond conductive layer 102 than in the center portion, it is morepreferable that the cross section be smaller on the anode side of thefirst conductive layer 101 and the second conductive layer 102. This isbecause the electric field on the side of the anode, where theresistance change layer 111 is oxidized, can be concentrated toefficiently supply oxygen from the lateral layer 112 to this portion ofelectric field concentration, thereby achieving more efficiently theeffect of reducing the forming voltage, improving the efficiency offorming, and reducing the reset current.

In the nonvolatile memory devices D141 and D142, the lateral layer 112having a higher oxygen concentration than the resistance change layer111 is illustratively provided on the lateral surface of the resistancechange layer 111. However, a lateral layer 113 including an oxide havinga lower free energy of formation than the resistance change layer 111may be provided on the lateral surface of the resistance change layer111. In this case, as described above, the cross section of theresistance change layer 111 along the X-Y plane may be smaller on oneside of the first conductive layer 101 and the second conductive layer102 than in the center portion.

It is noted that the configuration in which the cross section of theresistance change layer 111 is designed to be smaller on at least oneside of the first and second conductive layers 101 and 102 than in thecenter portion is applicable to any nonvolatile memory device accordingto the embodiments of the invention described above.

FIGS. 15A to 15D are schematic cross-sectional views in order of theprocesses, illustrating a method for manufacturing a nonvolatile memorydevice according to the sixth embodiment of the invention.

More specifically, FIGS. 15A to 15D illustrate a method formanufacturing the nonvolatile memory device D141.

As shown in FIGS. 15A and 15B, by a method similar to that describedwith reference to the first embodiment, a first conductive film 101 f, aresistance change film 111 f, and a second conductive film 102 f areformed on a substrate 100 s, and a mask 100 r is formed on the secondconductive film 102 f.

Then, the second conductive film 102 f, the resistance change film 111f, and the first conductive film 101 f are processed illustratively byRIE. Here, for instance, the RIE process is performed with a smalleramount of etching ions than in the condition described with reference tothe first embodiment.

Thus, as shown in FIG. 15C, the lateral surface of the resistance changefilm 111 f is tapered. Consequently, the cross section of the resistancechange film 111 f is made smaller near a second conductive layer 102than in the center portion.

Then, as shown in FIG. 15D, the lateral surface of the resistance changefilm 111 f is oxidized by the method described earlier to form a laterallayer 112 having a higher oxygen concentration than a resistance changelayer 111 on the lateral surface of the resistance change layer 111.

Thus, the nonvolatile memory device D141 can be fabricated.

FIGS. 16A and 16B are schematic cross-sectional views in order of theprocess, illustrating a method for manufacturing another nonvolatilememory device according to the sixth embodiment of the invention.

More specifically, FIGS. 16A and 16B illustrate a method formanufacturing the nonvolatile memory device D142.

For instance, after the processing described in FIGS. 15A to 15C isperformed, as shown in FIG. 16A, the resistance change film 111 f is wetetched with dilute hydrofluoric acid or the like. By this wet etching,the resistance change film 111 f is etched faster on the side of theresistance change film 111 f bordering the first conductive layer 101than in the center portion. Hence, the cross section of the resistancechange film 111 f is made smaller on the side of the first and secondconductive layers 101 and 102 than in the center portion.

Subsequently, as shown in FIG. 16B, the lateral surface of theresistance change film 111 f is oxidized by the method described earlierto form a lateral layer 112 having a higher oxygen concentration thanthe resistance change layer 111 on the lateral surface of the resistancechange layer 111.

Thus, the nonvolatile memory device D142 can be fabricated.

Seventh Embodiment

FIGS. 17A and 17B are schematic cross-sectional views illustrating theconfiguration of a nonvolatile memory device according to a seventhembodiment of the invention.

More specifically, FIG. 17A is a cross-sectional view taken along lineB-B′ of FIG. 17B, and FIG. 17B shows a cross section taken along lineA-A′ of FIG. 17A.

As shown in FIGS. 17A and 17B, also in a nonvolatile memory device D151according to this embodiment, a memory layer 60 includes a firstconductive layer 101, a second conductive layer 102, a resistance changelayer 111 provided between the first conductive layer 101 and the secondconductive layer 102, and a lateral layer 112 provided on the lateralsurface of the resistance change layer 111.

The stacking direction of the first conductive layer 101, the resistancechange layer 111, and the second conductive layer 102 is referred to asthe Z-axis direction. In this example, the memory layer 60 is providedon the major surface of a substrate 100 s, and the aforementionedstacking direction (Z-axis direction) is perpendicular to the majorsurface of the substrate 100 s.

The resistance change layer 111 is a layer whose electrical resistancechanges with at least one of the electric field applied thereto and thecurrent passed therein. The lateral layer 112 is a layer having a higheroxygen concentration than the resistance change layer 111. The laterallayer 112 functions as an oxygen supply layer for the resistance changelayer 111.

More specifically, the resistance change layer 111 and the lateral layer112 are both made of oxides, and the elements contained in theresistance change layer 111 are substantially the same as the elementscontained in the lateral layer 112. However, the content of oxygen inthe lateral layer 112 is higher than that in the resistance change layer111.

The lateral layer 112 has a higher electrical resistance than theresistance change layer 111. For instance, by the method described withreference to FIGS. 4A to 4D, the lateral surface of the film (resistancechange film 111 f), which serves as the resistance change layer 111 andthe lateral layer 112, is oxidized. Thus, the resistance change layer111 is formed in the center portion of the film, and the lateral layer112 is formed on the lateral surface of the film.

As shown in FIG. 17B, in this example, the cross-sectional shape of thememory layer 60 (resistance change layer 111 and lateral layer 112) cutalong the X-Y plane is circular (including ellipses and other oblatecircles). However, as described later, the invention is not limitedthereto. The cross-sectional shape of the memory layer 60 is arbitrary.

In the nonvolatile memory device D151, at least one of the composition,electrical resistance, and shape of the resistance change layer 111 andthe lateral layer 112 is adjusted so that the resistance change layer111 functions as a filament 111 p described with reference to FIGS. 3Aand 3B. Thus, the forming process for forming the filament 111 p can beomitted.

More specifically, as described earlier, the filament 111 p is formed bythe forming process after forming the memory layer 60. However, in thenonvolatile memory device D151, when the memory layer 60 is formed, theresistance change layer 111 being relatively rich in metal and havinglow electrical resistance is formed in a prescribed shape, and thelateral layer 112 functioning as an oxygen supply layer is provided onthe lateral surface thereof. Thus, the resistance change layer 111functioning as a filament 111 p can be formed without the formingprocess, and the forming process can be omitted.

In the forming process, it is often difficult to control the positionand shape of the filament 111 p formed in the resistance change layer111. This causes variation in the formation position and shape of thefilament 111 p, and may result in decreasing the reproducibility of thecharacteristics of the nonvolatile memory device. For instance, at thetime of forming, if a voltage is applied to the resistance change layer111 to pass a current therein, the flow of current starts to concentrateon the oxygen-deficient portion and the like of the resistance changelayer 111. This causes structure change due to Joule heat generation andforms a filament 111 p, lowering the resistance of the resistance changelayer 111. It is relatively difficult to control the density of suchdefects where the current concentrates. If the density of defects islow, numerous resistance change regions with fine size are generated,failing to achieve desired characteristics. Furthermore, if there isvariation in the size and the like of the filament 111 p where theresistance is lowered by current concentration, then the resistance issignificantly varied, which causes variation in voltage and current atset and reset time and makes it impossible to appropriately establishthe read voltage for reading the written data. Moreover, the resistancechange layer 111 may be destroyed, with the path between the first andsecond conductive layers 101 and 102 continuously turned into theconducting state, and fail to function as a resistance change layer 111.

In contrast, in the nonvolatile memory device D151, the filament 111 pis not formed by the forming process, but formed from the resistancechange layer 111 itself. Thus, the function of the filament 111 p can beimparted to the resistance change layer 111. Furthermore, because ofhigh controllability in the formation position and shape of theresistance change layer 111, high reproducibility is achieved in thecharacteristics of the nonvolatile memory device D151.

That is, the nonvolatile memory device D151 does not need the formingprocess. Furthermore, the electrical resistance of the resistance changelayer 111 can be suitably adjusted beforehand to reduce the resetcurrent to less than the allowable current of the driving circuits,protection diodes and the like. Thus, in the nonvolatile memory deviceD151, forming can be omitted, and the reset current can be reduced.

Furthermore, because of the small variation of resistance change in theresistance change layer 111, variation in voltage and current at set andreset time can be suppressed, and the controllability in characteristicscan be improved. Thus, a nonvolatile memory device with high performancecan be realized.

In the nonvolatile memory device D151 thus configured, for instance, theresistance change layer 111 can be narrowly designed so that theresistance change layer 111 has a smaller cross-sectional area than thelateral layer 112. More specifically, the ratio of the cross-sectionalarea of the resistance change layer 111 cut along the X-Y planeperpendicular to the Z axis versus the cross-sectional area of thelateral layer 112 can be designed to be lower than that in thenonvolatile memory device D101 illustrated in FIG. 1. For instance, thelength of the resistance change layer 111 in the cross-sectionaldirection (perpendicular to the Z-axis direction, or the stackingdirection) is shorter than the length of the lateral layer 112 in thecross-sectional direction. However, such shape relationship between theresistance change layer 111 and the lateral layer 112 is illustrativeonly, and the invention is not limited thereto. The shape relationshipbetween the resistance change layer 111 and the lateral layer 112 isarbitrary.

In the nonvolatile memory device D151, the oxygen concentration in theoxide of the resistance change layer 111 is decreased to reduce itselectrical resistance. Hence, the resistance change layer 111 isinitially in the low-resistance state LRS or the high-resistance stateHRS, and does not need the forming process. That is, without the formingprocess, the resistance change layer 111 assumes the condition ofincluding the low-resistance state LRS and the high-resistance state HRSas illustrated in FIG. 2, for instance.

Then, for instance, if an electric field (a voltage) is applied betweenthe first and second conductive layer 101 and 102 in the low-resistancestate LRS, the flow of current concentrates on the resistance changelayer 111 in the low-resistance state LRS. This current generates Jouleheat in the resistance change layer 111, increasing the temperature ofthe resistance change layer 111. When the temperature of the resistancechange layer 111 exceeds a certain temperature T1, oxygen migrates fromthe lateral layer 112, advances the oxidation reaction of the resistancechange layer 111, and increases the oxygen concentration in theresistance change layer 111. This increases electrical resistance in theresistance change layer 111, which is turned into the high-resistancestate HRS.

Such oxidation reaction is likely to occur near the anode, whichreceives electrons.

Here, when oxygen migrates from the lateral layer 112 to the resistancechange layer 111, the electrical resistance of the resistance changelayer 111 increases. However, simultaneously, the oxygen concentrationin the lateral layer 112 decreases, and the electrical resistance of thelateral layer 112 tends to decrease. The volume and oxygen concentrationof the lateral layer 112 are adjusted beforehand so that the electricalresistance of the lateral layer 112 is kept higher than the increasedelectrical resistance of the resistance change layer 111 when oxygen issupplied from the lateral layer 112 to the resistance change layer 111.

By such adjustment, when an electric field (a voltage) is applied againbetween the first and second conductive layers 101 and 102, the flow ofcurrent concentrates on the resistance change layer 111 in thehigh-resistance state HRS. Because the resistance change layer 111 is inthe high-resistance state HRS, Joule heat is easily generated even for asmall current flowing therein. Then, the current is passed until thetemperature reaches a temperature T2 higher than the temperature T1.This temperature T2 is a temperature allowing the progress of reductionreaction in which oxygen in the resistance change layer 111 migrates tothe lateral layer 112. Even when the resistance change layer 111generating heat reaches the temperature T2, the temperature of thelateral layer 112, resistant to current flow, is lower than thetemperature T2, although it increases due to heat conduction from theresistance change layer 111. Consequently, oxygen migrates from theresistance change layer 111 to the lateral layer 112, the oxygenconcentration in the resistance change layer 111 decreases to that inthe initial state, and the resistance change layer 111 returns to thelow-resistance state LRS. That is, the set operation is performed. It isnoted that as mentioned earlier, the set operation may be performed byan electric field applied to the resistance change layer 111.

Thus, the lateral layer 112 has a higher electrical resistance than theresistance change layer 111 in the high-resistance state HRS. That is,in any of the states with the oxygen concentration in the lateral layer112 varied by application of voltage to the first and second conductivelayers 101 and 102, the lateral layer 112 has a higher electricalresistance than the resistance change layer 111 (in the high-resistancestate HRS).

Also in this case, the resistance change layer 111 and the lateral layer112 can illustratively be made of an oxide of at least one selected fromSi, Ti, Ta, Nb, Hf, Zr, W, Al, Ni, Co, Mn, Fe, Cu, and Mo.

On the other hand, the first conductive layer 101 and the secondconductive layer 102 can be made of a material containing an elementwhose “standard free energy of oxide formation” has a smaller absolutevalue than that of the element except oxygen contained in the oxideincluded in the resistance change layer 111 (where the material includesa metal made of the former element, and an alloy, oxide, nitride, andoxynitride containing the former element).

For instance, elements whose “standard free energy of oxide formation”has a smaller absolute value than that of Hf include Ti, Nb, Ta, W, Moand the like. Elements whose “standard free energy of oxide formation”has a smaller absolute value than that of Ti include Nb, Ta, W, Mo andthe like.

Hence, in the case where the resistance change layer 111 is made of anoxide of Hf, the first conductive layer 101 and the second conductivelayer 102 can be made of at least one of an oxide, nitride, andoxynitride of Ti, Nb, Ta, W, Mo and the like. In the case where theresistance change layer 111 is made of an oxide of Ti, the firstconductive layer 101 and the second conductive layer 102 can be made ofat least one of an oxide, nitride, and oxynitride of Nb, Ta, W, Mo andthe like.

Furthermore, preferably, the conductive layer serving as an anode (oneof the first conductive layer 101 and the second conductive layer 102)is made of a material having high work function, whereas the conductivelayer serving as a cathode (the other of the first conductive layer 101and the second conductive layer 102) is made of a material having lowwork function. That is, the first conductive layer 101 has a higher workfunction than the second conductive layer 102.

For instance, in the case where the resistance change layer 111 is madeof an oxide of Ti, preferably, the conductive layer serving as an anodeis made of W or WN, and the conductive layer serving as a cathode ismade of Nb or NbN. By using such a combination between the conductivelayer having high work function and the conductive layer having low workfunction, the band gap of the resistance change layer 111 is bent,allowing the tunneling current to flow easily in the resistance changelayer 111 even under a low electric field. Thus, electric fieldconcentration can be caused at a lower electric field, making itpossible to reduce the voltage, which is limited by the breakdownvoltage of the driving circuit.

In the nonvolatile memory device D151, a clear boundary does not need toexist between the resistance change layer 111 and the lateral layer 112,but in the resistance change layer, it is only necessary that the oxygenconcentration is relatively higher on the lateral side than in thecenter portion in the plane perpendicular to the stacking direction.Thus, the lateral layer can also be regarded as a portion on the lateralside of the resistance change layer where the oxygen concentration isrelatively high.

Here, for instance, the diameter (length in a direction perpendicular tothe stacking direction) of the portion having low oxygen concentrationcan be designed to be smaller than the width (length in a directionperpendicular to the stacking direction) of the portion having highoxygen concentration, and the portion having low oxygen concentrationcan be regarded as the resistance change layer 111 functioning as afilament 111 p.

The nonvolatile memory device D151 as described above can be producedillustratively by the following method.

First, a first conductive film 101 f, a resistance change film 111 f,and a second conductive film 102 f are sequentially formed on asubstrate 100 s in which, for instance, driving circuit elements, aswell as wirings, plugs and the like connecting the driving circuitelements to the memory layer 60 are formed. These films can be formed byany of such processes as PVD (physical vapor deposition), CVD, and ALD.

In the film formation of the resistance change film 111 f, theelectrical resistance of the resistance change layer 111 is adjusted bytuning the oxygen composition. For instance, in the case where theresistance change layer 111 shaped like a cylinder with a diameter of 10nm and a film thickness of 20 nm is used to form an element in which acurrent of 10 μA (microamperes) flows at an applied voltage of 0.5 V(volts), the resistance of the cylindrical portion is 50 kΩ, and theresistance change film 111 f is formed by tuning the oxygen compositionso that, for instance, the resistance change film 111 f (resistancechange layer 111) has a specific resistance of 20 mΩcm. For instance,when a target containing the constituent element except oxygen of theresistance change film 111 f is used to perform chemical sputtering inan atmosphere containing Ar and O₂, the specific resistance of theresistance change film 111 f (resistance change layer 111) can beadjusted by controlling the partial pressure of O₂.

Then, a mask 100 r is used to process the first conductive film 101 f,the resistance change film 111 f, and the second conductive film 102 fillustratively by RIE. Thus, the lateral surface of the resistancechange film 111 f is formed. Then, the lateral surface of the resistancechange film 111 f is oxidized by heat treatment in an oxidizingatmosphere to form a lateral layer 112.

Here, for instance, in the case where the resistance change layer 111shaped like a cylinder with a diameter of 10 nm and a film thickness of20 nm is used to form an element in which a current of 10 μA flows at anapplied voltage of 0.5 V, the amount of oxidation of the resistancechange film 111 f is tuned by the oxygen partial pressure and heattreatment temperature so that a resistance change layer 111 shaped likea cylinder with a diameter of 10 nm and a film thickness of 20 nm isleft in the center portion.

Here, the first and second conductive layers 101 and 102 can be made ofa material containing an element whose “standard free energy of oxideformation” has a smaller absolute value than that of the element exceptoxygen contained in the resistance change layer 111 (resistance changefilm 111 f), and the temperature and oxygen partial pressure in theaforementioned oxidation heat treatment of the resistance change film111 f can be suitably selected so that in the oxidation heat treatment,the resistance change film 111 f is oxidized, but the first and secondconductive layers 101 and 102 are not oxidized. Furthermore, in theaforementioned oxidation heat treatment, only the resistance change film111 f can be selectively oxidized by using a mixed gas of an oxidizinggas and a gas capable of reducing the first and second conductive layers101 and 102.

Then, an interlayer insulating film is formed between the memory layers60, and wirings, plugs and the like connecting the driving circuitelements are formed. Thus, the nonvolatile memory device D151 can befabricated.

In forming the lateral layer 112, protrusions in a directionperpendicular to the stacking direction (Z-axis direction) may be formedfrom the lateral layer 112 and brought into contact with each otherbetween the adjacent elements (memory layers 60). To suppress this, forinstance, before the aforementioned oxidation heat treatment, theresistance change film 111 f may be etched by wet processing and thelike. This can suppress generation of the aforementioned protrusions.

In the foregoing description, the resistance change layer 111 is shapedlike a cylinder, and the lateral surface of the resistance change film111 f is oxidized from all directions in the X-Y plane. However,oxidation may be performed from part of the lateral surface. In thiscase, for instance, the resistance change layer 111 may not be shapedlike a cylinder. Thus, the shape of the resistance change layer 111 isarbitrary.

FIG. 18 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theseventh embodiment of the invention.

More specifically, FIG. 18 is a cross-sectional view corresponding tothe cross section taken along line A-A′ of FIG. 17A.

As shown in FIG. 18, in another nonvolatile memory device D152 accordingto this embodiment, the cross-sectional shape of a memory layer 60(resistance change layer 111 and lateral layer 112) cut along the X-Yplane is rectangular (square in this example).

Thus, the cross section of the resistance change layer 111 and thelateral layer 112 cut along a plane perpendicular to the stackingdirection can have an arbitrary shape, such as circles (including oblatecircles), rectangles and various other polygons, and polygons withrounded vertices.

For instance, the resistance change layer 111 is patterned by using themask 100 r as described with reference to, for instance, FIGS. 4A to 4D.Here, also in the case where the mask 100 r or a mask for forming it ispolygonal, for instance, the cross section of the resistance changelayer 111 may assume a shape including a curve in the patterningprocess, and the cross section of the resistance change layer 111 andthe lateral layer 112 also assumes a shape including a curveaccordingly.

FIGS. 19A and 19B are schematic cross-sectional views illustrating theconfigurations of other nonvolatile memory devices according to theseventh embodiment of the invention.

More specifically, FIGS. 19A and 19B are cross-sectional viewscorresponding to the cross section taken along line B-B′ of FIG. 17B.

As shown in FIG. 19A, in another nonvolatile memory device D153according to this embodiment, part of a lateral layer 112 is providedbetween first and second conductive layers 101 and 102 while being incontact with the lateral surface of a resistance change layer 111, andthe other part of the lateral layer 112 is provided in contact with thelateral surface of the first and second conductive layers 101 and 102.

As shown in FIG. 19B, in another nonvolatile memory device D154according to this embodiment, a lateral layer 112 is not providedbetween first and second conductive layers 101 and 102, but provided incontact with the lateral surface of a resistance change layer 111 andthe lateral surfaces of the first and second conductive layers 101 and102.

Thus, the lateral layer 112 only needs to be provided in contact withthe lateral surface of the resistance change layer 111.

Eighth Embodiment

FIG. 20 is a schematic cross-sectional view illustrating theconfiguration of a nonvolatile memory device according to an eighthembodiment of the invention.

More specifically, FIG. 20 is a cross-sectional view corresponding tothe cross section taken along line B-B′ of FIG. 17B.

As shown in FIG. 20, in a nonvolatile memory device D155 according tothis embodiment, the lateral layer 112 (the layer having a higher oxygenconcentration than the resistance change layer 111) in the nonvolatilememory device D151 is replaced by a lateral layer 113 (the layerincluding an oxide having a lower free energy of formation than aresistance change layer 111).

That is, in this example, the lateral layer 113 is made of an oxidehaving a lower free energy of formation than the element except oxygencontained in the oxide included in the resistance change layer 111.

For instance, the resistance change layer 111 is made of an oxide of Ti,and the lateral layer 113 is made of an oxide of Si. Also in this case,the lateral layer 113 has a higher electrical resistance than theresistance change layer 111.

Thus, as described with reference to the seventh embodiment, the need ofthe forming process is eliminated. Hence, the efficiency of forming isimproved, and the reset current can be reduced. Furthermore, because ofthe small variation of resistance change in the resistance change layer111, variation in voltage and current at set and reset time can besuppressed.

Also in this case, the resistance change layer 111 can be narrowlydesigned so that the resistance change layer 111 has a smallercross-sectional area than the lateral layer 113. For instance, thelength of the resistance change layer 111 in the cross-sectionaldirection (perpendicular to the Z-axis direction, or the stackingdirection) can be designed to be shorter than the length of the laterallayer 113 in the cross-sectional direction.

In the nonvolatile memory device D155, a clear boundary does not need toexist between the resistance change layer 111 and the lateral layer 113.That is, in the resistance change layer, the content of the elementwhose “standard free energy of oxide formation” has a relatively smallabsolute value (the element except oxygen) may be higher on the lateralside than in the center portion in the plane perpendicular to thestacking direction. For instance, the lateral layer can also be regardedas a portion on the lateral side of the resistance change layer wherethe content of the element whose “standard free energy of oxideformation” has a small absolute value is relatively higher than in thecenter portion.

Here, for instance, the diameter (length in a direction perpendicular tothe stacking direction) of the center portion having relatively lowcontent of the element whose “standard free energy of oxide formation”has a small absolute value can be designed to be smaller than the width(length in a direction perpendicular to the stacking direction) of theperipheral portion (lateral layer 113), and this center portion can beregarded as a resistance change layer 111 functioning as a filament 111p.

Also in this case, the oxygen concentration in the lateral layer 113 canbe made higher than that in the resistance change layer 111 to furtherenhance the effect of the lateral layer 113 as an oxygen supply layerfor the resistance change layer 111.

Furthermore, also in this case, the first conductive layer 101 and thesecond conductive layer 102 can be made of a material containing anelement whose “standard free energy of oxide formation” has a smallerabsolute value than the “standard free energy of oxide formation” of theelement except oxygen contained in the oxide included in the resistancechange layer 111 and the lateral layer 113 (where the material includesa metal made of the former element, and an alloy, oxide, nitride, andoxynitride containing the former element).

FIG. 21 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theeighth embodiment of the invention.

More specifically, FIG. 21 is a cross-sectional view corresponding tothe cross section taken along line B-B′ of FIG. 17B.

As shown in FIG. 21, in another nonvolatile memory device D156 accordingto this embodiment, part of a lateral layer 113 is provided betweenfirst and second conductive layers 101 and 102 while being in contactwith the lateral surface of a resistance change layer 111, and the otherpart of the lateral layer 113 is provided in contact with the lateralsurfaces of the first and second conductive layers 101 and 102.

Thus, the lateral layer 113 only needs to be provided in contact withthe lateral surface of the resistance change layer 111.

FIG. 22 is a schematic cross-sectional view illustrating theconfiguration of another nonvolatile memory device according to theeighth embodiment of the invention.

More specifically, FIG. 22 is a cross-sectional view corresponding tothe cross section taken along line B-B′ of FIG. 17B.

As shown in FIG. 22, in another nonvolatile memory device D157 accordingto this embodiment, a lateral layer 113 is not provided between firstand second conductive layers 101 and 102, but provided in contact withthe lateral surface of a resistance change layer 111 and the lateralsurfaces of the first and second conductive layers 101 and 102.

Furthermore, in this example, the nonvolatile memory device D157includes an interlayer insulating film 120, as described below, betweenadjacent memory layers 60.

More specifically, the nonvolatile memory device D157 includes a firstconductive layer 101, a second conductive layer 102, a first resistancechange layer 111, and a first lateral layer 113 provided on the lateralsurface of the first resistance change layer 111 and including an oxidehaving a lower free energy of formation than the first resistance changelayer 111.

The nonvolatile memory device D157 further includes a third conductivelayer 103, a fourth conductive layer 104, a second resistance changelayer 111 a, a second lateral layer 113 a provided on the lateralsurface of the second resistance change layer 111 a on the first laterallayer 113 side, and an interlayer insulating film 120 provided betweenthe first lateral layer 113 and the second lateral layer 113 a.

Furthermore, the interlayer insulating film 120 includes an oxide of anelement whose “standard free energy of oxide formation” has a smallerabsolute value than that of the element except oxygen contained in theoxide included in the first lateral layer 113 and the second laterallayer 113 a. That is, the first and second resistance change layers 111and 111 a, the first and second lateral layers 113 and 113 a, and theinterlayer insulating film 120, are made of oxides of an element withthe absolute value of the “standard free energy of oxide formation”decreasing in this order. This allows oxygen contained in the first andsecond lateral layers 113 and 113 a to easily migrate toward the firstand second resistance change layers 111 and 111 a rather than toward theinterlayer insulating film 120.

Furthermore, in the nonvolatile memory device D157, the interlayerinsulating film 120 is made of a compound having a lower oxygenconcentration than the first lateral layer 113 and the second laterallayer 113 a. For instance, the first and second resistance change layers111 and 111 a are made of an oxide of Ti, the first and second laterallayers 113 and 113 a are made of a compound of Si (SiO_(2+δ), where δ ispositive) having a relatively high oxygen concentration, and theinterlayer insulating film 120 is made of a compound of Si (SiO₂) havinga relatively low oxygen concentration. Hence, while maintaining highinsulation performance in the interlayer insulating film 120, it ispossible to relatively increase the oxygen concentration in the firstand second lateral layers 113 and 113 a. This allows oxygen contained inthe first and second lateral layers 113 and 113 a to easily migratetoward the first and second resistance change layers 111 and 111 a.

Thus, in the nonvolatile memory device D157 according to thisembodiment, the resistance change layer 111 substantially functions as afilament 111 p. Hence, the forming process can be omitted. Furthermore,because the interlayer insulating film 120 is made of the material asdescribed above, resetting is further facilitated, and the reset currentcan be further reduced.

It is noted that also in this case, the resistance change layer 111 canbe designed to be narrower than the lateral layer 113.

In this embodiment, the lateral layer 113 (the layer including an oxidehaving a lower free energy of formation than the resistance change layer111) may be replaced by a lateral layer 112 (the layer having a higheroxygen concentration than the resistance change layer 111).

The nonvolatile memory device D157 thus configured can illustratively befabricated on the basis of the method described with reference to FIGS.6A to 6D. More specifically, a first conductive film 101 f, a resistancechange film 111 f, and a second conductive film 102 f are formed in astacked manner and processed to form the lateral surface of theresistance change film 111 f. Then, on these layers, a film, whichserves as a lateral layer 113 (lateral layer 112), is formed, and afilm, which serves as an interlayer insulating film 120, is formedthereon and between the cells. Then, unnecessary films are removed asappropriate, and wirings, plugs and the like connecting the drivingcircuit elements are formed. Thus, the nonvolatile memory device D157 iscompleted.

By this method, even for a cell which is so downscaled that the regionfor both the resistance change layer 111 and the lateral layer 113(lateral layer 112) cannot be secured between the first and secondconductive layers 101 and 102, the resistance change layer 111 can beprovided between the first and second conductive layers 101 and 102, andthe lateral layer 113 (lateral layer 112) can be provided in contactwith the lateral surface of the resistance change layer 111. Thus, theaforementioned effect can be achieved.

The seventh and eighth embodiments have been described with reference toexamples in which the resistance change layer 111 is initially turnedinto the low-resistance state LRS or the high-resistance state HRS, andthe forming process can be omitted. However, the forming process may beperformed.

For instance, even in the case where the resistance change layer 111 isinitially in the low-resistance state LRS, if the electrical resistancein the low-resistance state LRS or the high-resistance state HRS isvaried initially, for instance, at the beginning of the switchingoperation, the forming process may be performed to reduce thisvariation. Also in this case, oxygen is supplied from the lateral layer112 (lateral layer 113) to the resistance change layer 111. Hence,forming is easier than in conventional techniques, and the formingvoltage can be reduced. Thus, the electrical resistance of theresistance change layer 111 can be stabilized by simple forming.

Ninth Embodiment

FIGS. 23A to 23C are schematic cross-sectional views illustrating theconfigurations of nonvolatile memory devices according to a ninthembodiment of the invention.

As shown in FIG. 23A, in a nonvolatile memory device D161 according tothis embodiment, the length (thickness) of the resistance change layer111 in the nonvolatile memory device D101, for instance, in the stackingdirection (Z-axis direction) is designed to be shorter (thinner) thanthe length (thickness) of the lateral layer 112 in the stackingdirection. The rest is similar to the nonvolatile memory device D101,and hence the description thereof is omitted.

As shown in FIG. 23B, in another nonvolatile memory device D162according to this embodiment, the length of a resistance change layer111 in the stacking direction (Z-axis direction) is designed to beshorter than the length of a lateral layer 112 in the stackingdirection, and simultaneously, the length (width) of the resistancechange layer 111 in a direction (e.g., X-axis direction or Y-axisdirection) perpendicular to the stacking direction is designed to beshorter than the length (width) of the lateral layer 112 in thedirection perpendicular to the stacking direction.

In the nonvolatile memory devices D161 and D162, because the thicknessof the resistance change layer 111 is thinner than that of the laterallayer 112, the electric field applied by the first and second conductivelayers 101 and 102 can be concentrated on the resistance change layer111, and the current is more likely to flow in the resistance changelayer 111 than in the lateral layer 112. Hence, the operating voltagecan be reduced, and the operating current can be reduced.

As shown in FIG. 23C, in another nonvolatile memory device D163according to this embodiment, the length of a resistance change layer111 in the stacking direction (Z-axis direction) is designed to beshorter than the length of a lateral layer 112 in the stackingdirection, and simultaneously, the length of the resistance change layer111 in a direction (e.g., X-axis direction or Y-axis direction)perpendicular to the stacking direction is designed to be shorter thanthe length of the lateral layer 112 in the direction perpendicular tothe stacking direction. Furthermore, the length of the resistance changelayer 111 in the direction perpendicular to the stacking direction islonger on the side of first and second conductive layers 101 and 102 (onthe end portion side) than in the center portion. That is, theresistance change layer 111 has a shape constricted in the centerportion in the aligning direction (Z-axis direction), and the diameterof the resistance change layer 111 in the center portion is narrowerthan that in the end portion.

Thus, the thickness of the resistance change layer 111 is made thinnerthan that of the lateral layer 112, and the center portion of theresistance change layer 111 is made narrower than the end portion, sothat oxygen can be efficiently exchanged in the narrowed portion. Thisfurther facilitates switching between the high-resistance state HRS andthe low-resistance state LRS, and the operating voltage and operatingcurrent can be further reduced.

The aforementioned nonvolatile memory devices D161 to D163 have beendescribed with reference to examples based on the lateral layer 112having a higher oxygen concentration than the resistance change layer111. However, the lateral layer 112 in the configuration illustrated inFIGS. 23A to 23C may be replaced by a lateral layer 113 including anoxide having a lower free energy of formation than the resistance changelayer 111. Also in this case, an effect similar to the foregoing isachieved.

The shape illustrated in FIGS. 23A to 23C, in which the length of theresistance change layer 111 in the stacking direction (Z-axis direction)is shorter than the length of the lateral layer 112 in the stackingdirection, can be formed illustratively by a method of using a mixed gasof an oxidizing gas and a gas capable of reducing the first and secondconductive layers 101 and 102 in the oxidation heat treatment afterprocessing the resistance change film 111 f into a prescribed shape.

Tenth Embodiment

A tenth embodiment of the invention relates to a cross-point nonvolatilememory device. Although this embodiment can be based on anyconfiguration of the nonvolatile memory devices described with referenceto the first to ninth embodiments, by way of example, a description isgiven of the case based on the configuration of the nonvolatile memorydevice D101.

FIGS. 24A to 24C are schematic views illustrating the configuration of anonvolatile memory device according to the tenth embodiment of theinvention.

More specifically, FIG. 24A is a schematic perspective view, FIG. 24B isa cross-sectional view taken along line A-A′ of FIG. 24A, and FIG. 24Cis a cross-sectional view taken along line B-B′ of FIG. 24A.

As shown in FIGS. 24A to 24C, a nonvolatile memory device D201 includesa plurality of stacked constituent memory layers 66.

Each of the constituent memory layers 66 includes a first wiring 50, asecond wiring 80 provided non-parallel to the first wiring 50, and astacked structure 65 provided between the first wiring 50 and the secondwiring 80. Each stacked structure 65 includes a memory layer 60 and arectifying element 70.

For instance, in the lowermost constituent memory layer 66 of thenonvolatile memory device D201, the first wirings 50 are word linesWL11, WL12, and WL13, and the second wirings 80 are bit lines BL11,BL12, and BL13. For instance, in the lowermost constituent memory layer66, the first wiring 50 aligns in the X-axis direction, and the secondwiring 80 aligns in the Y-axis direction orthogonal to the X-axisdirection. The first wiring 50, the second wiring 80, and the stackedstructure 65 provided therebetween are stacked in the Z-axis directionorthogonal to the X-axis direction and the Y-axis direction.

In the second lowest constituent memory layer 66, the first wirings 50are word lines WL21, WL22, and WL23, and the second wirings 80 are bitlines BL11, BL12, and BL13.

Furthermore, in the third lowest constituent memory layer 66, the firstwirings 50 are word lines WL21, WL22, and WL23, and the second wirings80 are bit lines BL21, BL22, and BL23. Furthermore, in the topmost(fourth lowest) constituent memory layer 66, the first wirings 50 areword lines WL31, WL32, and WL33, and the second wirings 80 are bit linesBL21, BL22, and BL23. It is noted that these word lines are genericallyreferred to as “word lines WL”, and these bit lines are genericallyreferred to as “bit lines BL”.

Although four constituent memory layers 66 are stacked in thenonvolatile memory device D201, the number of stacked constituent memorylayers 66 in the nonvolatile memory device according to this embodimentis arbitrary. Such a nonvolatile memory device can be provided on asemiconductor substrate, in which each of the constituent memory layers66 can be arranged parallel to the major surface of the semiconductorsubstrate. That is, a plurality of constituent memory layers 66 arestacked parallel to the major surface of the semiconductor substrate.

It is noted that an interlayer insulating film, not shown, is providedbetween the first wirings 50, between the second wirings 80, and betweenthe stacked structures 65 described above, and between each other.

In FIGS. 24A to 24C, to avoid complication, the first wirings 50 and thesecond wirings 80 in each of the constituent memory layers 66 areillustrated three for each. However, in the nonvolatile memory deviceD201 according to this embodiment, the number of first wirings 50 andthe number of second wirings 80 are arbitrary, and the number of firstwirings 50 may be different from the number of second wirings 80.

Furthermore, the first wirings 50 and the second wirings 80 are sharedby the adjacent constituent memory layers 66. More specifically, asillustrated in FIGS. 24A to 24C, the word lines WL21, WL22, and WL23 areshared by the overlying and underlying constituent memory layers 66, andthe bit lines BL11, BL12, and BL13 and the bit lines BL21, BL22, andBL23 are shared by the overlying and underlying constituent memorylayers 66. However, the invention is not limited thereto. The word linesWL and the bit lines BL may be independently provided in each of thestacked constituent memory layers 66. In the case where the word linesWL and the bit lines BL are independently provided in each of theconstituent memory layers 66, the aligning direction of the word line WLand the aligning direction of the bit line BL may be varied for each ofthe constituent memory layers 66.

In the foregoing, the first wiring 50 is a word line WL, and the secondwiring 80 is a bit line BL. However, the first wiring 50 may be a bitline BL, and the second wiring 80 may be a word line WL. That is, thebit line BL and the word line WL are interchangeable. In the following,a description is given of the case where the first wiring 50 is a wordline WL, and the second wiring 80 is a bit line BL.

As shown in FIGS. 24B and 24C, in each of the constituent memory layers66, the stacked structure 65 including the memory layer 60 and therectifying element 70 is provided at a portion (cross point) where thefirst wiring 50 and the second wiring 80 cross three-dimensionally. Thememory layer 60 at each cross point serves as one memory unit, and thestacked structure 65 including this memory layer 60 serves as one cell.

In the example shown in FIGS. 24B and 24C, the rectifying element 70 isprovided on the first wiring 50 side, and the memory layer 60 isprovided on the second wiring 80 side. However, the memory layer 60 maybe provided on the first wiring 50 side, and the rectifying element 70may be provided on the second wiring 80 side. Furthermore, the stackingorder of the rectifying element 70 and the memory layer 60 with respectto the first wiring 50 and the second wiring 80 may be varied for eachof the constituent memory layers 66. Thus, the stacking order of therectifying element 70 and the memory layer 60 is arbitrary.

The rectifying element 70 can be based on various diodes, such as a pindiode including stacked films made of a polycrystalline silicon layerdoped with p-type and n-type impurity, a Schottky diode including aSchottky barrier formed at a metal-semiconductor interface, and an MIM(metal insulator metal) diode having a metal/insulator/metal stackedstructure. Alternatively, the rectifying element 70 can be based ontransistors and various other rectifying elements. In this example,although the rectifying element 70 is stacked on the memory layer 60 atthe intersection between the first wiring 50 and the second wiring 80,the rectifying element 70 may be provided in a portion other than theintersection between the first wiring 50 and the second wiring 80.

The memory layer 60 has one of the configurations described withreference to the aforementioned first to ninth embodiments.

The nonvolatile memory device D201 can further include word lines WL(first wirings 50) and bit lines BL (second wirings 80) provided so asto sandwich the aforementioned resistance change layer 111 (memory layer60), which is subjected to at least one of application of voltage andpassage of current through the word lines WL and the bit lines BL.

At least one of a first conductive layer 101 and a second conductivelayer 102 may double as at least one of the word line WL and the bitline BL.

The nonvolatile memory device D201 can further include a rectifyingelement 70 provided between at least one of the word line WL and the bitline BL on the one hand, and the memory layer 60 including theaforementioned resistance change layer 111 on the other. At least one ofthe first conductive layer 101 and the second conductive layer 102 maydouble as at least part of the rectifying element 70.

That is, the configuration of the first conductive layer 101 and thesecond conductive layer 102 is arbitrary as long as they are conductorshaving the function of applying voltage to and passing current in theresistance change layer 111.

FIG. 25 is a schematic perspective view illustrating the configurationof another nonvolatile memory device according to the tenth embodimentof the invention.

As shown in FIG. 25, a nonvolatile memory device D202 according to thisembodiment is an example with eight constituent memory layers 66 stackedtherein.

The nonvolatile memory device (memory layer 60) of the first to ninthembodiments and a rectifying element 70 are provided between a word lineWL and a bit line BL.

Here, the rectifying element 70 at the odd stage and the rectifyingelement 70 at the even stage are designed to have opposite rectifyingcharacteristics so that the word line WL and the bit line BL are sharedat the odd stage and the even stage.

In the nonvolatile memory device D202 having such a structure, theintegration density of memory cells can be increased by a relativelysimple configuration. Furthermore, because each memory cell includes arectifying element 70, the bypass current passing through memory cellsother than the selected memory cell can be suppressed.

An example method for manufacturing a nonvolatile memory deviceaccording to this embodiment is now described. In the following, by wayof example, a description is given of the case of using theconfiguration of the memory layer 60 described with reference to thefirst embodiment. Furthermore, in this example, a description is givenof the case where the first and second conductive layers 101 and 102 donot double as other layers or wirings.

FIGS. 26A to 26F are schematic cross-sectional views in order of theprocess, illustrating a method for manufacturing a nonvolatile memorydevice according to the tenth embodiment of the invention.

FIGS. 27A to 27E are schematic cross-sectional views in order of theprocesses continuing from FIG. 26F.

It is noted that the depicted direction of FIGS. 26E and 26F and FIGS.27A to 27E is rotated 90 degrees around the Z-axis direction from thedepicted direction of FIGS. 26A to 26D.

First, as shown in FIG. 26A, first-layer first wirings 50 are formedillustratively on a substrate 100 s provided with driving circuitelements (not shown). The first wiring 50 is shaped like a stripaligning illustratively in the X-axis direction, and an interlayerinsulating film 120 a such as silicon oxide film is buried between thefirst wirings 50.

A p-type semiconductor film 71 f, a polycrystalline silicon film 72 f,and an n-type semiconductor film 73 f, which are to constitute arectifying element 70, are stacked on the first wiring 50 and theinterlayer insulating film 120 a. Subsequently, a first conductive film101 f, a resistance change film 111 f, and a second conductive film 102f are stacked.

Subsequently, as shown in FIG. 26B, for instance, by RIE processingusing a mask 100 r having a prescribed shape, the p-type semiconductorfilm 71 f, the polycrystalline silicon film 72 f, the n-typesemiconductor film 73 f, the first conductive film 101 f, the resistancechange film 111 f, and the second conductive film 102 f are processedinto a pillar. Thus, the lateral surface of the resistance change film111 f is formed, and a rectifying element 70, a first conductive layer101, and a second conductive layer 102 are formed.

Then, as shown in FIG. 26C, the lateral surface of the resistance changefilm 111 f is oxidized to form a lateral layer 112 and a resistancechange layer 111.

Then, as shown in FIG. 26D, an interlayer insulating film 120 is buriedin the gap between the stacked structures each including the rectifyingelement 70, the first conductive layer 101, the resistance change layer111, the lateral layer 112, and the second conductive layer 102. Theinterlayer insulating film 120 can illustratively be a silicon oxidefilm.

As shown in FIG. 26E, an interlayer insulating film 120 b such assilicon oxide film is formed on the interlayer insulating film 120 andthe second conductive layer 102, and RIE processing, for instance, isperformed using a mask 100 ra having a prescribed shape.

Thus, as illustrated in FIG. 26F, a trench 121 aligning in the Y-axisdirection is formed in the interlayer insulating film 120 b to exposethe upper surface of the second conductive layer 102.

Then, as shown in FIG. 27A, a conductive film is buried in the trench121 and planarized illustratively by CMP (chemical mechanical polishing)to form a first-layer second wiring 80.

Furthermore, as shown in FIG. 27B, an n-type semiconductor film 73 f, apolycrystalline silicon film 72 f, and a p-type semiconductor film 71 f,which are to constitute a second-layer rectifying element 70, are formedin this order on the second wiring 80 and the interlayer insulating film120 b. Then, a second conductive film 102 f, a resistance change film111 f, and a first conductive film 101 f are formed thereon.

Here, as described above, the stacking order of the p-type semiconductorfilm 71 f, the polycrystalline silicon film 72 f, and the n-typesemiconductor film 73 f, which constitute the first-layer rectifyingelement 70, and the stacking order of the p-type semiconductor film 71f, the polycrystalline silicon film 72 f, and the n-type semiconductorfilm 73 f, which constitute the second-layer rectifying element 70, areopposite to each other. Furthermore, the stacking order of the firstconductive film 101 f, the resistance change film 111 f, and the secondconductive film 102 f in the first layer, and the stacking order of thefirst conductive film 101 f, the resistance change film 111 f, and thesecond conductive film 102 f in the second layer, are also opposite toeach other. Here, the second layer may be formed in the order of, forinstance, the second conductive film 102 f, the resistance change film111 f, the first conductive film 101 f, the n-type semiconductor film 73f, the polycrystalline silicon film 72 f, and the p-type semiconductorfilm 71 f.

Then, as shown in FIG. 27C, for instance, by RIE processing using a mask100 r having a prescribed shape, the n-type semiconductor film 73 f, thepolycrystalline silicon film 72 f, the p-type semiconductor film 71 f,the second conductive film 102 f, the resistance change film 111 f, andthe first conductive film 101 f are processed into a pillar. Thus, arectifying element 70, a first conductive layer 101, and a secondconductive layer 102 in the second layer are formed.

Then, as shown in FIG. 27D, the lateral surface of the resistance changefilm 111 f is oxidized to form a lateral layer 112 and a resistancechange layer 111.

Subsequently, as shown in FIG. 27E, an interlayer insulating film 122such as silicon oxide film is buried in the gap between the stackedstructures each including the rectifying element 70, the firstconductive layer 101, the resistance change layer 111, the lateral layer112, and the second conductive layer 102 in the second layer.Subsequently, second-layer wirings are formed by a similar method.

Then, a necessary number of constituent memory layers 66 are formed by asimilar method.

Thus, the nonvolatile memory device D201 and the nonvolatile memorydevice D202 can be fabricated.

In the nonvolatile memory device D201 and the nonvolatile memory deviceD202, if the memory layer 60 is based on the configuration other thanthat of the nonvolatile memory device D101, the aforementioned method isadapted by interchanging the order of processes, changing the condition,or adding necessary processes.

The foregoing has described the method for processing, layer by layer,the stacked films constituting a memory layer 60 (first conductive film101 f, resistance change film 111 f, and second conductive film 102 f),and the films constituting a rectifying element 70 (e.g., p-typesemiconductor film 71 f, polycrystalline silicon film 72 f, and n-typesemiconductor film 73 f). However, for instance, two adjacentconstituent memory layers 66 may be collectively processed.

For instance, the first wiring film 50 f, the films constituting arectifying element 70, and the stacked films constituting a memory layer60 in the first layer are processed, for instance, into a strip aligningin the X-axis direction, and an interlayer insulating film is buriedbetween the strips. Then, a first-layer second wiring film 80 f, filmsconstituting a second-layer rectifying element 70, stacked filmsconstituting a second-layer memory layer 60, and a second-layer firstwiring film 50 f are formed. Then, the films constituting a first-layerrectifying element 70, and the stacked films constituting a first-layermemory layer 60, as well as the interlayer insulating film, thefirst-layer second wiring film 80 f, the films constituting asecond-layer rectifying element 70, the stacked films constituting asecond-layer memory layer 60, and the second-layer first wiring film 50f may be processed along the Y-axis direction, so that the filmsconstituting a first-layer rectifying element 70 and the stacked filmsconstituting a first-layer memory layer 60 are processed into a pillar,whereas the interlayer insulating film, the first-layer second wiringfilm 80 f, the films constituting a second-layer rectifying element 70,the stacked films constituting a second-layer memory layer 60, and thesecond-layer first wiring film 50 f are processed into a strip aligningin the Y-axis direction.

In this case, by performing oxidation treatment of the resistance changefilm 111 f after each processing process, a lateral layer 112 can beformed illustratively on each of the lateral surface parallel to theX-axis direction and the lateral surface parallel to the Y-axisdirection.

In the foregoing, a description has been given of the case where thenonvolatile memory device according to this embodiment is a cross-pointnonvolatile memory device. However, the embodiment of the invention isnot limited thereto. For instance, it is also applicable to anonvolatile memory device in which a resistance change layer is used inpart of a MIS transistor.

For instance, it is possible to further include a MIS (metal insulatorsemiconductor) transistor including a gate electrode and a gateinsulating layer sandwiching the memory layer 60 of the nonvolatilememory device according to one of the first to ninth embodiments so thatat least one of application of voltage to the resistance change layer111 and passage of current in the resistance change layer 111 isperformed through the gate electrode.

More specifically, the configuration can further include a first andsecond second-conductivity-type semiconductor regions provided in afirst-conductivity-type semiconductor substrate, afirst-conductivity-type semiconductor region between the first andsecond second-conductivity-type semiconductor regions, and a gateelectrode for controlling conduction/non-conduction between the firstand second second-conductivity-type semiconductor regions, wherein thememory layer 60 (at least one of the first and second conductive layers101 and 102, the resistance change layer 111, and the lateral layers 112and 113) of the nonvolatile memory device according to one of the firstto ninth embodiments is located between the gate electrode and thefirst-conductivity-type semiconductor region, so that at least one ofapplication of voltage to the resistance change layer 111 of thenonvolatile memory device and passage of current in the resistancechange layer 111 is performed through the gate electrode.

Thus, the MIS transistor using the resistance change characteristics ofthe resistance change layer 111 can be used as a memory element.

Thus, the nonvolatile memory device according to the embodiment of theinvention can be variously modified.

Eleventh Embodiment

FIG. 28 is a flow chart illustrating a method for manufacturing anonvolatile memory device according to an eleventh embodiment of theinvention.

As shown in FIG. 28, the method for manufacturing a nonvolatile memorydevice according to this embodiment begins with stacking, on a substrate100 s, a first conductive film 101 f serving as a first conductive layer101, a resistance change film 111 f whose electrical resistance changeswith at least one of the electric field applied thereto and the currentpassed therein, and a second conductive film 102 f serving as a secondconductive layer 102 (step S110). That is, for instance, the processingdescribed with reference to FIG. 4A or 26A is performed.

Here, the resistance change film 111 f can be made of various metaloxides described above. The first conductive film 101 f and the secondconductive film 102 f are preferably made of a material containing anelement whose “standard free energy of oxide formation” has a smallerabsolute value than that of the element except oxygen contained in theoxide included in the resistance change film 111 f. This material caninclude a metal made of a second element whose “standard free energy ofoxide formation” has a smaller absolute value than that of a firstelement except oxygen contained in the oxide included in the resistancechange film 111 f, and an alloy, oxide, nitride, and oxynitridecontaining the second element.

Then, the first conductive film 101 f, the resistance change film 111 f,and the second conductive film 102 f are processed to form the lateralsurface of the resistance change film 111 f (step S120). That is, forinstance, the processing described with reference to FIG. 4B or FIG. 26Bis performed.

For instance, the first conductive film 101 f, the resistance changefilm 111 f, and the second conductive film 102 f are cut in a directionparallel to the stacking direction (e.g., Z-axis direction) of the firstconductive film 101 f, the resistance change film 111 f, and the secondconductive film 102 f. Here, the cutting direction only needs to benon-perpendicular to the stacking direction as long as the resistancechange film 111 f is exposed.

Then, the exposed lateral surface of the resistance change film 111 f isoxidized (step S130). Thus, the oxygen concentration is made higher onthe lateral side than in the center portion of the cross section of theresistance change film 111 f cut along a plane perpendicular to thestacking direction (e.g., Z-axis direction). For instance, theprocessing described with reference to FIG. 4C or FIG. 26C is performed.

Thus, a nonvolatile memory device can be manufactured, which includes alateral layer 112 provided on the lateral surface of the resistancechange layer 111 and having a higher oxygen concentration than theresistance change layer 111. That is, a resistance change nonvolatilememory device can be manufactured, in which the forming voltage isreduced, the efficiency of forming is improved, and the reset current isreduced.

In the specification of the application, “perpendicular” and “parallel”refer to not only strictly perpendicular and strictly parallel but alsoinclude, for example, the fluctuation due to manufacturing processes,etc. It is sufficient to be substantially perpendicular andsubstantially parallel.

The embodiments of the invention have been described with reference toexamples. However, the invention is not limited to these examples. Forinstance, various specific configurations of the components, such as theconductive layer, conductive film, resistance change layer, resistancechange film, lateral layer, interlayer insulating film, memory layer,word line, bit line, wiring, and rectifying element constituting thenonvolatile memory device are encompassed within the scope of theinvention as long as those skilled in the art can similarly practice theinvention and achieve similar effects by suitably selecting suchconfigurations from conventionally known ones.

Furthermore, any two or more components of the examples can be combinedwith each other as long as technically feasible, and such combinationsare also encompassed within the scope of the invention as long as theyfall within the spirit of the invention.

Furthermore, those skilled in the art can suitably modify and implementthe nonvolatile memory device and the method for manufacturing the samedescribed above in the embodiments of the invention, and all thenonvolatile memory devices and methods for manufacturing the same thusmodified are also encompassed within the scope of the invention as longas they fall within the spirit of the invention.

Furthermore, those skilled in the art can conceive various modificationsand variations within the spirit of the invention, and it is understoodthat such modifications and variations are also encompassed within thescope of the invention. For instance, those skilled in the art cansuitably modify the above embodiments by addition, deletion, or designchange of components, or by addition, omission, or condition change ofprocesses, and such modifications are also encompassed within the scopeof the invention as long as they fall within the spirit of theinvention.

1. A nonvolatile memory device comprising: a first conductive layer; asecond conductive layer; a first resistance change layer providedbetween the first conductive layer and the second conductive layer andhaving an electrical resistance changing with at least one of an appliedelectric field and a passed current; and a first lateral layer providedon a lateral surface of the first resistance change layer and having anoxygen concentration higher than an oxygen concentration in the firstresistance change layer.
 2. The device according to claim 1, furthercomprising: a third conductive layer opposed to a lateral surface of thefirst conductive layer; a fourth conductive layer opposed to a lateralsurface of the second conductive layer; a second resistance change layerprovided between the third conductive layer and the fourth conductivelayer and having an electrical resistance changing with at least one ofan applied electric field and a passed current; a second lateral layerprovided on a lateral surface of the second resistance change layer on aside of the first lateral layer and including at least one of a compoundhaving a higher oxygen concentration than the second resistance changelayer and an oxide of an element having a smaller absolute value ofstandard free energy of oxide formation than an element except oxygencontained in an oxide included in the second resistance change layer;and an interlayer insulating film provided between the first laterallayer and the second lateral layer and including an oxide of an elementhaving a smaller absolute value of standard free energy of oxideformation than the element contained in the oxide included in the firstlateral layer and the second lateral layer.
 3. The device according toclaim 1, wherein at least part of the first lateral layer is providedbetween the first conductive layer and the second conductive layer. 4.The device according to claim 1, wherein the first resistance changelayer includes M_(x)O_(y), and the first lateral layer includesM_(x1)O_(y1) (y1>y), the M being a transition metal element, the O beingoxygen.
 5. The device according to claim 1, wherein the first resistancechange layer includes A_(α)M_(β)O_(γ), and the first lateral layerincludes A_(α1)M_(β1)O_(γ1) (γ1>γ), the A being a transition metalelement, the M being a transition metal element, the O being oxygen. 6.The device according to claim 1, wherein the first lateral layerincludes a metal oxide having a substantially stoichiometric compositionratio, and the first resistance change layer includes the metal oxidewith a proportion of oxygen reduced to 90% or less as compared with thefirst lateral layer.
 7. The device according to claim 1, wherein thefirst resistance change layer and the first lateral layer include anoxide of at least one selected from the group consisting of Si, Ti, Ta,Nb, Hf, Zr, W, Al, Ni, Co, Mn, Fe, Cu, and Mo.
 8. The device accordingto claim 1, wherein the first conductive layer and the second conductivelayer include a material containing an element having a smaller absolutevalue of standard free energy of oxide formation than an element exceptoxygen contained in an oxide included in the first resistance changelayer.
 9. The device according to claim 1, wherein the first conductivelayer and the second conductive layer include at least one of W, Ta, Cu,TiN, TaN, WC, and highly doped silicon.
 10. The device according toclaim 1, wherein a width of the first resistance change layer along afirst direction is smaller than a width of the lateral layer along thefirst direction, the first direction being perpendicular to a stackingdirection from the first conductive layer toward the second conductivelayer.
 11. The device according to claim 1, wherein a work function ofthe first conductive layer is different from a work function of thesecond conductive layer.
 12. A nonvolatile memory device comprising: afirst conductive layer; a second conductive layer; a first resistancechange layer provided between the first conductive layer and the secondconductive layer and having an electrical resistance changing with atleast one of an applied electric field and a passed current; and a firstlateral layer provided on a lateral surface of the first resistancechange layer and including an oxide of an element having a smallerabsolute value of standard free energy of oxide formation than anelement except oxygen contained in an oxide included in the firstresistance change layer.
 13. The device according to claim 12, furthercomprising: a third conductive layer opposed to a lateral surface of thefirst conductive layer; a fourth conductive layer opposed to a lateralsurface of the second conductive layer; a second resistance change layerprovided between the third conductive layer and the fourth conductivelayer and having an electrical resistance changing with at least one ofan applied electric field and a passed current; a second lateral layerprovided on a lateral surface of the second resistance change layer on aside of the first lateral layer and including at least one of a compoundhaving a higher oxygen concentration than the second resistance changelayer and an oxide of an element having a smaller absolute value ofstandard free energy of oxide formation than an element except oxygencontained in an oxide included in the second resistance change layer;and an interlayer insulating film provided between the first laterallayer and the second lateral layer and including an oxide of an elementhaving a smaller absolute value of standard free energy of oxideformation than the element contained in the oxide included in the firstlateral layer and the second lateral layer.
 14. The device according toclaim 12, wherein at least part of the first lateral layer is providedbetween the first conductive layer and the second conductive layer. 15.The device according to claim 12, wherein the first resistance changelayer and the first lateral layer include an oxide of at least oneselected from the group consisting of Si, Ti, Ta, Nb, Hf, Zr, W, Al, Ni,Co, Mn, Fe, Cu, and Mo.
 16. The device according to claim 12, whereinthe first conductive layer and the second conductive layer include atleast one of W, Ta, Cu, TiN, TaN, WC, and highly doped silicon.
 17. Thedevice according to claim 12, wherein a width of the first resistancechange layer along a first direction is smaller than a width of thelateral layer along the first direction, the first direction beingperpendicular to a stacking direction from the first conductive layertoward the second conductive layer.
 18. The device according to claim12, wherein a work function of the first conductive layer is differentfrom a work function of the second conductive layer.
 19. A method formanufacturing a nonvolatile memory device, comprising: stacking, on asubstrate, a first conductive film serving as a first conductive layer,a resistance change film having electrical resistance changing with atleast one of an applied electric field and a passed current, and asecond conductive film serving as a second conductive layer; etching thefirst conductive film, the resistance change film, and the secondconductive film to form a lateral surface of the resistance change film;and oxidizing the lateral surface to make an oxygen concentration on aside of the lateral surface higher than a oxygen concentration in acenter portion of a cross section of the resistance change film cutalong a plane perpendicular to a stacking direction of the stacking. 20.The method according to claim 19, wherein a width of the center portionof the resistance change film along a first direction is smaller than awidth of a portion on the side of the lateral surface with the higheroxygen concentration, the first direction being perpendicular to thestacking direction from the first conductive layer toward the secondconductive layer.